MacKINNON, Senior Circuit Judge:
Appellant Daphne Essex appeals her conviction for possession of heroin with intent to distribute. 21 U.S.C. § 841(a). At the start of the trial, the defense stipulated to proceeding with a jury of 11 if it became necessary to do so. But a full jury heard all the evidence, began deliberations, and adjourned over the weekend. One juror failed to appear on Monday morning and the court — without finding that there was any reason for excusing him, and over defense objection — permitted the 11 remaining jurors to continue deliberations and to return a verdict.
The government admits the defendant objected that it was “not proven necessary” to continue without the juror and that the court overruled said objection. Since there was no finding of any reason that it was “necessary” to proceed with less than a full jury, the denial of the defendant’s right to a unanimous verdict of the 12 jurors constituted (1) an obvious violation of the terms of the stipulation, and (2) a violation of Fed.R.Crim.P. 23(b) and 31(a). Even assuming the error was not properly raised before the district court, we would find this procedure to be a defect affecting appellant’s substantial right and reviewable under the so-called “plain error” rule, Fed.R.Crim.P. 52(b). We accordingly reverse.1
[835]*835I. Facts
Shortly after the jury was selected, a juror who had been stricken peremptorily by the defense was accidentally seated among the 12 jurors. Only one alternate had been selected; the rest of those examined on voir dire had been dismissed. The improper seating was discovered before the trial started, and the following exchange then occurred:
THE COURT: Mr. Goodbread, I understand that the Government is willing to accept alternate No. One in place of No. 12, and that’s agreeable to you, is it?
MR. GOODBREAD [Appellant’s Counsel]: It is, your Honor.
THE COURT: That means we proceed without an alternate and it is understood that in the event we should have anything happen to one of them, they are unable to come, if it is not less than one juror you are willing to proceed with 11?
MR. GOODBREAD: That’s correct, your Honor.
THE COURT: That’s agreeable to your client?
THE DEFENDANT: Yes.
THE COURT: Very well. Is it agreeable to the Government?
MR. O’MALLEY [Government Counsel]: It is agreeable to the Government, your Honor, but this is an issue which, as the court well knows, has been litigated many times.
If we could have a formal waiver from Miss Essex, that is, to indicate that she has been advised that she has an absolute right to have 12 jurors and that if she waives it she waives any right to appeal that issue, and she must be satisfied with a verdict of 11.
THE COURT: Do you understand, Miss Essex, that you are entitled to a jury of 12 and you wouldn’t [sic] certainly have it if we had it. At the moment you are going to have 12.
I am just saying that in the event something should happen to one of them, we don’t have any alternates.
THE DEFENDANT: Yes, Ma’am.
THE COURT: So if something should happen to one, we would proceed with 11. Is that your understanding and you agree to that?
THE DEFENDANT: Yes, Ma’am, I do.
THE COURT: Very well.
(Tr. 42-43) (emphasis added). Thereupon, the previously stricken juror was dismissed and replaced by the sole alternate.
The case proceeded to trial. None of the jurors was excused during the trial phase. The parties rested on a Friday and the jury retired to deliberate. The jurors deliberated until about 6:00 p.m., when they were given the option to continue deliberations during the evening or to return Monday morning. They voted to return on Monday. In excusing them, to return at 9:30 on Monday morning, the Court said to counsel: “It will not be necessary for you to be here at 9:30 on Monday. The clerk will check them in when they are all here and they will continue with their deliberations” (Tr. 394) (emphasis added).
On Monday, only 11 of the 12 jurors appeared at 9:30. Appellant’s counsel, notified of the situation by telephone, immediately objected to allowing the jury to proceed. No record was made of the objection that counsel was called upon to make — by telephone — first to the court’s secretary, and then to the judge personally. The trial judge, over such defense objection, construed appellant’s oral stipulation as sufficient to cover the situation and directed the jury to resume its deliberations with only 11 jurors. So far as the record indicates, the court made no investigation regarding the missing juror and did not determine the reason for the juror’s failure to appear.
A. The Government’s Concession
We are not completely handicapped by a silent record, however, because appellant’s contemporaneous objections are explained in her brief, and the Government in its brief concedes their correctness:
As explained in her brief, appellant’s counsel, who was at an administrative hearing, communicated his objections to [836]*836accepting a verdict from eleven jurors in a telephone conversation with the trial judge. Brief for Appellant at 7-8. The contents of that call are not a part of the record on appeal, but for the purposes of this appeal we credit appellant’s representations that her counsel objected to accepting a verdict of less than twelve jurors. Just before the verdict was returned, appellant’s counsel noted for the record his objection to accepting a verdict from eleven rather than twelve jurors (Tr. 397).
Brief for Government at 7 n. 3 (emphasis added).
The contemporaneous objections “communicated [to] the trial judge,” id., as “explained in [appellant’s] brief” that the government “credits” are set forth in the margin.2 The specific admission by the Government in its brief is important. It concedes that appellant contemporaneously objected “[a]s explained in her brief.” This concession thus admits that counsel objected to the Court’s ruling on the ground that it would deprive appellant of her right that her “conviction [be achieved] by unanimity of those jurors who actually heard and deliberated the case.” The Government’s concession also admits that counsel objected to the court’s proceeding with only 11 jurors on the ground that the stipulation only agreed to 11 jurors “if necessary, ” and “[t]hat turned out not to be necessary” (emphasis added). Appellant also asserted that such procedure was not “proven necessary.” Despite these timely objections, the court ruled that the 11 remaining jurors could continue their deliberations on the ground that there was “no difference” in whether the juror’s absence was proven necessary or not proven necessary. The dissent essentially takes the same position. The 11 jurors returned a unanimous verdict of guilty, and defense counsel again objected to the jury procedure.3 He alluded to the issue again in his motion for new trial.4
[837]*837It does not appear from the record that either appellant or the Government requested the court to try and locate the missing juror — or that the court ever attempted to locate him or determine the reason for his absence. The parties stated at oral argument that, so far as they knew, the reason for the missing juror’s absence was never determined. The transcript does not indicate that the court ever ruled on the objection it took under advisement (Tr. 400-01).
A. The Rule Requiring a Jury of Twelve.
At the time of trial, Fed.R.Crim.P. 23(b) provided: [838]*838(Emphasis added.)5 The stipulation here was conditional, and comes under the second clause, which contrary to the dissent’s assertions, see Dissent at 853, requires a finding of some just cause that makes it necessary to excuse a juror.
[837]*837Juries shall be of 12 but at any time before verdict the parties may stipulate in writing with the approval of the court that the jury shall consist of any number less than 12 or that a valid verdict may be returned by a jury of less than 12 should the court find it necessary to excuse one or more jurors for any just cause after trial commences.
[838]*838The Rule also expressly required a written waiver, but this was not done. The court and the parties should have complied with the Rule and executed a written waiver. Had they done so, much of our difficulty might have been avoided. But we do not rest our reversal on the erroneous failure to execute a written waiver. The requirement of a writing is “procedural,” and in situations where the defendant makes an oral waiver in open court with advice of counsel, and where it is clear that the subsequent action taken by the court followed the terms of the waiver, the failure to comply with Rule 23(b) is harmless. United States v. Ricks, 475 F.2d 1326, 1328 (D.C.Cir.1973) (per curiam); United States v. Smith, 523 F.2d 788, 791-92 (5th Cir.1975), cert. denied, 424 U.S. 973, 96 S.Ct. 1475, 47 L.Ed.2d 742 (1976); United States v. Lane, 479 F.2d 1134, 1136 (6th Cir.), cert. denied, 414 U.S. 861, 94 S.Ct. 78, 38 L.Ed.2d 112 (1973). We accordingly rule that the failure to reduce the waiver to writing was harmless error.6
Since a spontaneous oral waiver customarily lacks the clarity, specificity, and assurance of adequate consideration of a written waiver, the circumstances must be examined closely, and must plainly evidence the express and knowledgeable consent of the defendant7 to accepting a verdict of less than 12 jurors.
An examination of the cases in which oral waivers have been held valid is illustrative. In Ricks, the oral waiver at issue was made after the juror did not appear; it is clear that the waiver extended to continuing the trial. The original stipulation agreed to by the defendant in Rogers v. United States, 319 F.2d 5, 7 (7th Cir.1963), cert. denied, 375 U.S. 989, 84 S.Ct. 524, 11 L.Ed.2d 475 (1964), was unambiguous, and was renewed after the juror failed to ap[839]*839pear. Similarly, in Lane the waiver was made after the juror was excused. This is not to imply that only an oral waiver after the juror is excused is valid,8 but in each of these eases it was clear that the defense had intelligently and knowledgeably consented to continuing the trial with 11 jurors under the conditions that necessitated that departure from prescribed procedure.
The stipulation in this case is just as clear. One claim asserted by appellant is that the verdict is improper because she had not agreed that the stipulation would apply during jury deliberations. This broad claim is without merit. Appellant unquestionably agreed to accept a verdict of 11 jurors if it became necessary to excuse one juror during deliberations. The stipulation did not distinguish between the different phases of the trial, nor did it purport to specify any time for its expiration. If a juror was properly excused at any time before verdict, the verdict necessarily would be that of 11 jurors, and such a verdict would have been permissible under the terms of the stipulation and the Rules.
But the stipulation was not an agreement to accept a possible jury of 11 under any and all circumstances. The real issue in this case is whether, under the stipulation and the Rules, the court properly continued the jury’s deliberations without the missing juror.9
B. The Effect of the Stipulation
A conditional stipulation, under the second clause of Rule 23(b), that a valid verdict can be returned by a jury of less than 12 requires a finding by the court that it is necessary to excuse the juror for just cause. A stipulation that the trial will continue if something “should happen” to a juror and he is excused because he becomes “ill,” or he is “unable to come” — i.e., this stipulation — is contingent upon the court finding the existence of the occurrence of the specified condition and upon the court’s finding that it is “necessary” to excuse the juror.
The Advisory Committee Notes which accompanied Rule 23(b) in its original form made clear the types of situations in which jurors should be excused: the Rule is “useful in case it becomes necessary during the trial to excuse a juror owing to illness or for some other cause.” Id. (emphasis added). After the 1977 amendment, the Notes explain that the Rule “makes it clear that the parties ... may enter into an agreement to have the case decided by less than 12 jurors if one or more jurors are unable or disqualified to continue” (emphasis added). The terms “unable” or “disqualified” define what is intended by the term “just cause.” The Rule permits verdicts of less than 12 if (1) it is necessary to excuse a juror for just cause, and (2) there is a stipulation. The terms of the stipulation itself recognized this fact.
Rule 23(b) stipulations thus are contingent upon satisfying this condition precedent. The judge’s statements that formed the basis of the stipulation provided that appellant would be “willing to proceed with 11” jurors “in the event we should have anything happen to them, they are unable to come” (Tr. 43). Thereafter, the judge repeated the condition that the waiver would operate “if something should happen” to one of the jurors. Id. The stipulation thus would not become operative unless a juror’s absence was due to some ascertainable happening that rendered him “unable” or “disqualified” to participate. [840]*840A juror who takes “French leave” 10 cannot be said to have had anything “happen” to him. The waiver, by its terms, did not abrogate either the trial court’s duty to investigate the non-appearance of a juror and make a finding as to the cause, or appellant’s right, in the absence of determined good cause, to the unanimous verdict of all the jurors who heard the evidence, were instructed by the Court, and retired to deliberate on the verdict.11 Because no finding of just cause was made, the stipulation was not complied with, and therefore cannot excuse the violations discussed below.
C. The Rule Requiring a Unanimous Verdict
Rule 31(a) of the Federal Rules of Criminal Procedure requires: “The verdict shall be unanimous.” As indicated above, 12 jurors began deliberations and the verdict was returned by only 11 jurors. There is nothing in the transcript between the recess of the jury of 12 at 6:05 p.m. on Friday, November 19, 1983 (Tr. 395), and the return of the verdict of 11 at 11:22 a.m. on Monday, November 22, 1983 (Tr. 397)— much less any finding of a justifiable reason for accepting the verdict of 11 jurors. And, as noted above, the Government admits that defense counsel objected to the court’s permitting the jury to continue its deliberations with only 11 jurors on the ground “the Government should be required to convince all of the jurors it had attempted to persuade ... twelve in this case” (R. 19-5). While appellant’s objections were not precisely articulated, the substance of her objection made it clear that she did not waive her right to a unanimous verdict. The waiver went to the number of jurors, not to the requirement of unanimity. She had stipulated to the waiver of one juror — but since it had not been found necessary to excuse any juror, that waiver could not be construed as a waiver of unanimity. There is a well recognized distinction between the waiver of a jury of 12, and the waiver of unanimity. United States v. Pachay, 711 F.2d 488, 492 (2d Cir.1983); United States v. Vega, 447 F.2d 698, 701 (2d Cir.1971) (counsel was willing to accept a jury of 11, but would not accept a non-unanimous verdict; hold-out juror excused), cert. denied, 404 U.S. 1038, 92 S.Ct. 712, 30 L.Ed.2d 730 (1972).
Excusing a juror during deliberations jeopardizes the right to unanimity protected by Rule 31(a). This Rule was designed to protect the rights of defendants under the Sixth Amendment to the United States Constitution. See Fed.R.Crim.P. 23, Notes of Advisory Committee subd. (a). When the juror has been excused on a finding of just cause and the defendant has consented, the dangers are minimized and the procedure permitted by Rule 23(b) does not violate Rule 31(a). But when, as here, there is no finding by the court that it is “necessary ... for just cause” to excuse a juror during deliberations, a defendant is denied the right to a unanimous jury verdict that is protected by Rule 31(a). Significantly, four circuits — the Second, Third, Sixth, and Ninth — have held that the intent of the drafters of Rule 31(a) not to permit waiver of unanimity, even with the consent of the defendant, is evident from the preparatory history of the Rule. See United States v. Pachay, 711 F.2d 488, 490-91 (2d Cir.1983) (citing United States v. Lopez, 581 F.2d 1338, 1341-42 (9th Cir.1978); United States v. Scalzitti, 578 F.2d 507, 510-12 (3d Cir.1978); Hibdon v. United States, 204 F.2d 834 (6th Cir.1953); 8A Moore’s Federal Practice ¶ 31.02[1], at 31-3 (2d ed. 1982); 3 C. Wright, Federal Practice and Procedure § 511, at 3-5 (2d ed. 1982)). The dissent completely ignores this feature of the Rule.
[841]*841However, because appellant’s stipulation did not purport to waive the unanimity requirement, and appellant never consented to such waiver, it is not necessary in this case to rely on these authorities. The right to a unanimous jury is derived from the federal rules and the Sixth Amendment. United States v. Morris, 612 F.2d 483, 488-89 (10th Cir.1979); United States v. Scalzitti, 578 F.2d 507, 511 (3d Cir.1978); United States v. Gipson, 553 F.2d 453, 456 (5th Cir.1977). In Apodaca v. Oregon, 406 U.S. 404, 92 S.Ct. 1628, 32 L.Ed.2d 184 (1972), and Johnson v. Louisiana, 406 U.S. 356, 92 S.Ct. 1620, 32 L.Ed.2d 152 (1972), five justices were in agreement that in federal criminal cases juries were required by the Sixth Amendment to be unanimous. Appellant’s counsel, before the jury returned its verdict, several times objected to construing her stipulation as a waiver of unanimity (Tr. 397; R. 19-5 to 19-7). In fact, he expressly pointed out that the verdict would lack “unanimity” (R. 19-6, Brief for Appellant at 6-8). That is sufficient to support her claim of error. This objection is also repeated in her appeal. Brief for Appellant at 6-8, 10-18, 20-30.12
As the Ninth Circuit has explained,
The dynamics of the jury process are such that often only one or two members express doubt as to a view held by a majority at the outset of deliberations. A rule which insists on unanimity furthers the deliberative process by requiring the minority view to be examined and, if possible, accepted or rejected by the entire jury. The requirement of jury unanimity thus has a precise effect on the fact-finding process, one which gives particular significance and conclusiveness to the jury’s verdict.
United States v. Lopez, 581 F.2d 1338, 1341 (9th Cir.1978). This reasoning applies with equal force to a situation where, as here, a juror has absented himself for no valid reason: in both cases there is a danger that dissenting views may not be heard, debated, and resolved by the process of arriving at a unanimous verdict. The requirement of unanimity for a verdict in a criminal case “is inextricably interwoven with” the standard of proof beyond a reasonable doubt. Hibdon v. United States, 204 F.2d 834, 838 (6th Cir.1953) (“there cannot be a verdict supported by proof beyond a reasonable doubt if one or more jurors remain reasonably in doubt as to guilt”). The requirement of unanimity would lose a great deal of its force if, as the dissent implies, jurors may opt out at will. Permitting this erosion would lessen the prosecution’s burden of convincing the entire membership of the jury. The record here cannot support a conclusion that appellant waived her right to a unanimous verdict. We accordingly rule that her right to a unanimous jury verdict was violated.
D. The Verdict of 11 Jurors
Was “it necessary to excuse one ... juror[] for any just cause,” in accordance with the condition of the stipulation or the Rule? While counsel, contrary to the statement of the dissent, did object promptly by telephone to continuing delib[842]*842erations with only eleven jurors, there is no indication that in his telephone call he requested a search or inquiry for the missing juror — or even that he was informed that such inquiry had not been made. But it was the court’s clear duty to determine the whereabouts of the missing juror and make a finding that there was just cause for excusing him. The explanation in appellant’s brief credited by the Government, the statements of the Government prosecutor, and the emptiness of the record cannot support a statement that the reason for the juror’s absence was ever determined —and there is no support whatsoever for the suggestion that the court ever made a finding that just cause existed to excuse the missing juror.
The objections made by appellant were broad enough to raise the issue that the court erred by failing to find “just cause.” Counsel did not, and he was not required to, use those precise words. The objection was to the substantial variance from normal jury procedure in criminal trials that the court indicated it proposed to follow without a finding that such ruling was “necessary.” No magic words are required to constitute an objection. By analogy to objections to evidence, the objection to procedure, the specific ground for the objection being apparent from the context, was sufficient: “(1) a substantial right [was] affected, and (2) the nature of the error was called to the attention of the judge, so as to alert [her] to the proper course of action.” Fed.R.Evid. 103(a), Notes of Advisory Committee subd. (a).
The court considered it was in a position to rule immediately, and it overruled defendant’s objections by permitting the jury of 11 to proceed with its deliberations. In thus permitting the jury of 11 to proceed and return a verdict, the court treated the stipulation to waive a jury of 12, if necessary, as sufficient to waive a jury of 12 even if not necessary. Defendant’s objection was timely, positive, and specific, and the error was clear and obvious. Both objections were again raised in open court before the jury returned (Tr. 397), and in haec verba in defendant’s motions for a mistrial or new trial (R. 19-5b, ¶¶ 16-17). There is nothing to the dissent’s assertion that the substance of the objection was not raised at trial. Dissent at 846, 847, 848, 850, 853. A finding of good cause necessity was required to avoid a violation of Rule 23(b) and no such finding was ever made.
Since (1) the record is silent, and (2) the court must “find” just cause on the record, and (3) the case must be affirmed or reversed on the record, and (4) there is nothing in the record to support the court’s action, the case must be reversed. The stipulation was the only possible basis for proceeding without 12 jurors, and nothing in the record supports a finding that the terms of the stipulation were complied with. Contrary to the implication of the dissent, there is nothing novel about deciding cases on the record or the absence thereof.13 The record in a criminal case must support the judgment, and the court is just as responsible as counsel for seeing [843]*843that the record supports its rulings. The absence of the required finding in the record is a substantial error. The argument that the judge is not ordinarily required to establish the cause for the juror’s absence, see Dissent at 854 n. 42, flies directly in the face of Rule 23(b).
We cannot condone the loose jury practices in which the dissent finds no error. The dissent rests on loose and highly speculative possibilities and assumptions that have no support in the record.14 We find that the court denied defendant her right to the unanimous verdict of 12 jurors without any finding that anything did “happen” to any one of them so that he was “unable” to participate. That is violating the stipulation, not relying upon it. Such trial conduct also violated Rules 23(b) and 31(a).15
IV. Defects Affecting Substantial Rights and Plain Error
From the foregoing it is sufficiently clear that appellant’s basic contentions were in substance made timely and contemporaneously at trial, and the Government so admits. But even assuming that counsel did not specifically ground his objection to the procedure and verdict in the formal terminology of Rule 23(b) or 31(a), or that, as the dissent argues, the objections suffered from other defects, the error was serious enough to require reversal. Fed.R. Crim.P. 52(b) provides:
Plain errors or defects affecting substantial rights may be noticed although they were not brought to the attention of the court.
(Emphasis added.) In United States v. Atkinson, 297 U.S. 157, 160, 56 S.Ct. 391, 392, 80 L.Ed. 555 (1936), the Supreme Court described “plain errors” as follows:
In exceptional circumstances, especially in criminal eases, appellate courts, in the public interest, may, of their own motion, notice errors to which no exception has been taken, if the errors are obvious, or if they otherwise seriously affect the fairness, integrity or public reputation of judicial proceedings.
Thus, under the Rule, an appellate court may ground its decision on defects affecting substantial rights — or plain errors— even though the defect or error was not raised at all. In fact, the rule is frequently applied when the error or defect is not brought to the attention of the trial court. See, e.g., Silber v. United States, 370 U.S. 717, 718, 82 S.Ct. 1287, 1288, 8 L.Ed.2d 798 (1962) (per curiam); Brotherhood of Carpenters v. United States, 330 U.S. 395, 412, 67 S.Ct. 775, 784, 91 L.Ed. 973 (1947); Brasfield v. United States, 272 U.S. 448, 450, 47 S.Ct. 135, 136, 71 L.Ed. 345 (1926); Mahler v. Eby, 264 U.S. 32, 45, 44 S.Ct. 283, 288, 68 L.Ed. 549 (1924).
Plain error has been variously defined, and it depends upon the facts of each particular case. The words “plain error” are self-explanatory to a certain extent, and include “defects affecting substantial rights.” Fed.R.Crim.P. 52(b). The dissent fails to recognize fully this basic feature of the Rule.
The Fifth Circuit defined the circumstances in which plain errors would be noticed as “those involving serious deficiencies which affect the fairness, integrity or [844]*844public reputation of the judicial proceedings or which constitute obvious error.” United States v. Brown, 548 F.2d 1194, 1207 (5th Cir.1977). We defined it in similar terms in United States v. McCord, 509 F.2d 334 (D.C.Cir.1974) (en banc), cert. denied, 421 U.S. 930, 95 S.Ct. 1656, 44 L.Ed.2d 87 (1975):
[T]he doctrine of plain error encompasses those errors which are obvious, affect the substantial rights of the accused and if uncorrected would be an affront to the integrity and reputation of judicial proceedings.
Id. at 341 n. 10 (citing Silber v. United States, 370 U.S. 717, 718, 82 S.Ct. 1287, 1288, 8 L.Ed.2d 798 (1962); Johnson v. United States, 318 U.S. 189, 199-201, 63 S.Ct. 549, 554-55, 87 L.Ed. 704 (1943); United States v. Atkinson, 297 U.S. 157, 160, 56 S.Ct. 391, 392, 80 L.Ed. 555 (1936)). Other definitions: “Plain error is one so clearly prejudicial to substantial rights as to jeopardize the very fairness and integrity of the trial.” Rink v. United States, 388 A.2d 52, 56 (D.C.App.1978). And plain error is that which “affected [appellant’s] ‘substantial rights’ resulting in a miscarriage of justice.” West v. United States, 359 F.2d 50, 53 (8th Cir.), cert. denied, 385 U.S. 867, 87 S.Ct. 131, 17 L.Ed.2d 94 (1966).
The application of the plain error rule is within the sound discretion of the court. Billeci v. United States, 290 F.2d 628, 629 (9th Cir.1961). It is to be applied sparingly to errors vital to defendants. United States v. Frady, 456 U.S. 152, 163 n. 3, 102 S.Ct. 1584, 1589 n. 3, 71 L.Ed.2d 816 (1982) (citing Wiborg v. United States, 163 U.S. 632, 658, 16 S.Ct. 1127, 1137, 41 L.Ed. 289 (1896)).
As noted previously, federal defendants are entitled to (1) juries of 12, unless they are properly waived in accordance with Rule 23(b), and (2) unanimous verdicts by the jurors who deliberated, unless a juror was properly excused in accordance with Rule 23(b).16 Rule 23(b) requires a finding of just cause before it is operable.
A. The Right Affected
The obvious and substantial right of appellant that was denied is her right to a unanimous verdict by the jury of 12 who heard her case and began their deliberations. There is nothing in this trial record, or in the contentions of the Government, that indicates the juror in this case had anything happen to him that gave him any justifiable reason to absent himself. Appellant speculates that the juror may have been a lone holdout for innocence in the face of a hostile pro-conviction majority, and for that reason stayed home rather than take part in the proceedings. There is no evidence that such was the case — there is no evidence of any reason whatsoever— but that is exactly one of the possibilities the Rules are designed to avoid. The defendant’s right to a jury trial, with all its historic and procedural protections, is too important to allow jurors to opt out by simply failing to show up after the commencement of deliberations. The rights of both the defendant and the prosecution under the Rule and the stipulation require that a reasonable investigation be made and the court find it to be neces[845]*845sary for some stated reason constituting good cause to excuse the juror.
The trial court has a great deal of discretion in deciding to excuse a juror for cause. An appellate court ordinarily will not second-guess such a determination, but the parties agree that, to the best of their knowledge, no determination of any reason for the juror’s absence was made in this case. We have demonstrated that this failure violated (1) the stipulation, (2) Federal Rules 23(b) and 31(a), and (3) basic obligations of the court to supervise the jury. Such failures constituted defects which denied appellant’s substantial right, in the absence of determined good cause, to the unanimous verdict of the 12 jurors to whom the determination of the cause was duly submitted.
B. Prejudice
The claim is made by the dissent that appellant has shown no prejudice. But no further prejudice need be shown than that the court did not comply with the stipulation and Rule 23(b), and that appellant was denied her right to have her case decided by the unanimous verdict of the 12 jurors who heard the case. In cases involving secret jury deliberations it is virtually impossible for a defendant to demonstrate actual prejudice. Courts therefore have determined that the potential for serious harm and the interest of the defendant— and the public — in fair, unbiased and secret deliberations are so great that no evidentiary showing of actual prejudice, or of defense counsel’s objection to the internal functioning of the jury of which he could not possibly be informed, is required.
For example: Without regard to actual prejudice, it has been held to constitute error for a trial court to permit a prosecution witness merely to enter the jury room during deliberations in order to play a tape for the jurors, United States v. Pittman, 449 F.2d 1284, 1286 (1971); or to place the jury in the custody of sheriffs’ deputies who are testifying at the trial, even when there is no indication that they have spoken to the jurors, Turner v. Louisiana, 379 U.S. 466, 472-74, 85 S.Ct. 546, 549-50, 13 L.Ed.2d 424 (1965). It is plain error for the trial judge to call the jury back from deliberations and ask them how they are numerically divided, even when there is no showing that it had any influence on the jury. See Brasfield v. United States, 272 U.S. 448, 450, 47 S.Ct. 135, 136, 71 L.Ed. 345 (1926) (“We deem it essential to the fair and impartial conduct of the trial that the inquiry itself should be regarded as grounds for reversal.”); Government of the Virgin Islands v. Romain, 600 F.2d 435, 437 (3d Cir.1979); United States v. Noah, 594 F.2d 1303, 1304 (9th Cir.1979) (per curiam). Similarly, it is plain error for the trial court to permit an alternate juror to retire to the jury room for deliberations with the other jurors, even for a period of as little as 45 minutes and even when the alternate says nothing. See United States v. Chatman, 584 F.2d 1358, 1361 (4th Cir.1978) (although evidence against defendant was overwhelming, reversal was required). We believe that prejudice is inherent when a court permits a jury of 12 to continue deliberations and return a verdict with only 11 jurors, without making the finding required by the Rule and the stipulation. The dissent can cite no decision that supports excusing a juror (except in accordance with a contemporaneous agreement) without a finding of a stated reason.
Underlying the dissent’s plain error analysis is the apparent notion that the Rule cannot be applied because it asserts that no “miscarriage of justice” occurred in this case. But where, as here, the prejudice is inherent in the error complained of, the defendant is not required to prove that he is innocent, or that the outcome of the trial would have been different, had the error not been made. Brasfield, supra, 272 U.S. at 450, 47 S.Ct. at 136. Chatman, supra, 584 F.2d at 1361. The evidence amassed against appellant was considerable — but it is well settled that even defendants who are obviously guilty are entitled to the basic procedural safeguards of a fair trial. See, e.g., Brewer v. Williams, 430 U.S. 387, 406, 97 S.Ct. 1232, 1243, 51 L.Ed.2d 424 (1977) (right to counsel during non-coercive questioning); Estes v. Texas, 381 U.S. 532, 542-44, 85 S.Ct. 1628, 1632-33, 14 L.Ed.2d 543 (1965) (broadcast of trial [846]*846jeopardized fairness); In re Murchison, 349 U.S. 133, 137-38, 75 S.Ct. 623, 625-26, 99 L.Ed. 942 (1955) (judge who functions as “one-man grand jury” cannot preside at contempt trial arising from grand jury proceedings); Rideau v. Louisiana, 373 U.S. 723, 726-27, 83 S.Ct. 1417, 1419, 10 L.Ed.2d 663 (television broadcast of defendant’s confession).
In our judgment, as outlined above, the defects affected appellant’s substantial rights, and thus justify reversal under Rule 52(b). We disagree with the dissent that this court is powerless to correct errors of such magnitude.
The judgment of the trial court is reversed, and a new trial ordered.17
Judgment accordingly.
The abbreviation "Tr." refers to the transcript; “R.,” to the Court’s record file; and to the Joint Appendix.