TRAYNOR, C.J.

Defendant appeals from a judgment of conviction entered upon a verdict finding him guilty of assault with intent to commit rape (Pen. Code, § 220).

The victim testified that while she was waiting for a bus in Burlingame at 5 a.m., July 20, 1964, defendant sought to induce her to engage in sexual intercourse. When she rebuffed him, he threatened to use his knife to compel submission. She saw no knife, but fled screaming, and defendant ran beside her repeatedly whispering, "Walk. Don't run." When a newspaper boy appeared on the otherwise deserted street defendant disappeared.

Defendant was arrested on September 9, 1964, and taken to the San Mateo Police Department, where the victim identified him in a lineup as her assailant. The victim also indicated that she could identify her assailant's voice. She was placed in a room next to the interrogation room, and defendant was asked to repeat phrases recited by the police. Defendant refused to cooperate and remained silent.

Police officers testified that they advised defendant of his right to counsel and of his right to remain silent and testified to his responses to their questions. They also testified that he refused to participate in the voice identification test. Defendant contends that introduction of the evidence of his refusal to participate in a voice identification test and the prosecutor's comments thereon violated his constitutional privilege against self-incrimination.

[1] The privilege against self-incrimination applies to evidence of "communications or testimony" of the accused, but not to "real or physical" evidence derived from him. (E.g., Schmerber v. California (1966) 384 U.S. 757, 764 [16 L.Ed.2d 908, 86 S.Ct. 1826]; Holt v. United States (1910) 218 U.S. 245, 252-253 [54 L.Ed. 1021, 31 S.Ct. 2]; Gilbert v. United States (9th Cir. 1966) 366 F.2d 923; United States v. Denno (2d Cir. 1966) 355 F.2d 731, 738; Rigney v. Hendrick (3d Cir. 1965) 355 F.2d 710, 713-714; Kennedy v. United States (D.C. Cir. 1965) 353 F.2d 462, 466; Caldwell v. United States (8th Cir. 1964) 338 F.2d 385, 389; People v. Lopez (1963) 60 Cal.2d 223, 243-244 [ 32 Cal.Rptr. 424, 384 P.2d 16]; People v. Duroncelay (1957) 48 Cal.2d 766, 770 [ 312 P.2d 690]; People v. Trujillo (1948) 32 Cal.2d 105, 112-113 [ 194 P.2d 681]; People v. Zavala (1966) 239 Cal.App.2d 732, 738-739 [ 49 Cal.Rptr. 129]; 8 Wigmore, Evidence (McNaughton rev. 1961) § 2265, p. 386; Model Code of Evidence (1942) rule 201 (2); Uniform Rules of Evidence (1953) rule 23 (3).) The results of voice identification tests fall within the category of real or physical evidence. ( Gilbert v. United States, supra; Rigney v. Hendrick, supra; People v. Lopez, supra; Wigmore, op. cit., supra; cf. People v. Graves (1966) 64 Cal.2d 208 [ 49 Cal.Rptr. 386, 411 P.2d 114], cert. den., 385 U.S. 883 [17 L.Ed.2d 111, 87 S.Ct. 175].) [2] In such a test, the speaker is asked, not to communicate ideas or knowledge of facts, but to engage in the physiological processes necessary to produce a series of articulated sounds, the verbal meanings of which are unimportant. The sounds alone are elicited for identification purposes through characteristics such as pitch, tone, intonation, accent, and word stress. [3] The speech patterns of individuals are distinctive physical characteristics that serve to identify them just as do other physical characteristics such as color of eyes, hair, and skin, physical build and fingerprints.

Voice identification testimony is the product of an observable physical characteristic made by an independent witness. It is the very type of objective factual evidence, independent of information communicated by the accused, that the privilege encourages police to seek. Moreover, independent identification testimony, unlike testimonial evidence derived from the accused, raises no question of reliance on the veracity of the accused. Any attempt by a suspect to disguise his voice is apt to be detected readily by those persons present who can compare the sample with his normal voice. Furthermore, there is no risk that one could be coerced into falsely accusing himself. It is difficult to imagine how a suspect could be induced to impersonate an unknown voice to incriminate himself.

[4] It has been urged that the privilege reflects an ultimate sense of fairness that prohibits the state from demanding assistance of any kind from an individual in penal proceedings taken against him. The privilege includes no such prohibition. Criminal proceedings are replete with instances where at least passive cooperation of an accused may be constitutionally required.

A suspect asked to speak for voice identification is not subjected to the same psychological pressures said to be generated by a demand for testimony. [5] It is no more unfair to ask a suspect to speak for voice identification than to ask him to appear in a lineup for visual identification. The psychological pressures are reduced to the same degree, through a limitation of alternatives. Deceit is improbable; the simple choice for a guilty person is between conduct likely to expose incriminating evidence and inferences as to guilt likely to flow from a successful refusal to participate.

A related view of the individual interest protected by the privilege focuses on the right of privacy. ( United States v. Grunewald (2d Cir. 1956) 233 F.2d 556, 581-582 (Frank, J., dissenting) revd. 353 U.S. 391 [1 L.Ed.2d 931, 77 S.Ct. 963, 62 A.L.R.2d 1344]; Ratner, Consequences of Exercising the Privilege Against Self-Incrimination (1957) 24 U.Chi.L.Rev. 472, 488-489.) The Fifth Amendment right of privacy protects at least uncommunicated thoughts and has been extended to preclude compelled production of private papers and documents. ( Boyd v. United States (1886) 116 U.S. 616 [29 L.Ed. 746, 6 S.Ct. 524].) [6] A voice test, however, contemplates no such intrusion into privacy; no disclosure of thought or privately held information is requested. One's voice is hardly of a private nature. It is constantly exposed to public observation and is merely another identifying physical characteristic.

It thus appears that an extension of the privilege to voice identification would serve none of the purposes of the privilege. It would only exclude evidence of considerable importance when visual identification is doubtful or impossible. The masked robber, the telephone extortionist, and the attacker in the night may all seek refuge behind an extension of the privilege that would do little to further the welfare of accused persons in general. Denial of access to a pertinent identifying trait can only weaken a system dedicated to the ascertainment of truth.

We do not leave the individual unprotected. The need for protection is greater in confession cases where the risk of police overzealousness is comparatively great because self-incriminating statements are the most persuasive evidence of guilt. Testimony by a witness resulting from a purported identification is less conclusive and there is therefore less incentive for police to use unwarranted pressure in obtaining the evidence. Nevertheless, it bears emphasis that, as in the case of all police procedures for the securing of nonprivileged evidence, fundamental principles of fairness and due process are always applicable to prevent abuse. (See Rochin v. California (1952) 342 U.S. 165 [96 L.Ed. 183, 72 S.Ct. 205, 25 A.L.R.2d 1396]; People v. Matteson (1964) 61 Cal.2d 466 [ 39 Cal.Rptr. 1, 393 P.2d 161].)

Even though evidence obtained from a voice identification is not within the privilege against self-incrimination, the question remains whether evidence and comment on a refusal to take such a test is admissible. [7] It is clear that "it is impermissible to penalize an individual for exercising his Fifth Amendment privilege when he is under police custodial interrogation." ( Miranda v. Arizona (1966) 384 U.S. 436, 468, fn. 37 [16 L.Ed.2d 694, 86 S.Ct. 1602, 10 A.L.R.3d 974].) This doctrine is a logical extension ( People v. Cockrell (1965) 63 Cal.2d 659 [ 47 Cal.Rptr. 788, 408 P.2d 116]) of the rule of Griffin v. California (1965) 380 U.S. 609 [14 L.Ed.2d 106, 85 S.Ct. 1229], prohibiting comment on the failure of an accused to testify at trial. Comment on refusal to testify was held to be "a penalty imposed by courts for exercising a constitutional privilege. It cuts down on the privilege by making its assertion costly." ( Griffin v. California, supra, at p. 614.) [8] Such a rule is not applicable when, as in this case, the defendant has no constitutional right to refuse to speak solely for purposes of voice identification.

[9] Nor was defendant's refusal to "display his voice" itself a testimonial communication. It was circumstantial evidence of consciousness of guilt, and like similar evidence, such as escape from custody ( People v. Otis (1959) 174 Cal.App.2d 119 [ 344 P.2d 342]), false alibi ( People v. Allison (1966) 245 Cal.App.2d 568, 576 [ 54 Cal.Rptr. 148]), flight ( People v. Hoyt (1942) 20 Cal.2d 306 [ 125 P.2d 29]), suppression of evidence ( People v. Burton (1961) 55 Cal.2d 328 [ 11 Cal.Rptr. 65, 359 P.2d 433]), and failure to respond to accusatory statements when not in police custody (see 19 Cal.Jur.2d, Evidence, § 401, p. 141 et seq.), its admission does not violate the privilege. Moreover, as in the foregoing examples, the evidence did not result from a situation contrived to produce conduct indicative of guilt. Unlike the superstitious tests described by Wigmore and their modern successor, the lie detector, that have as their sole purpose the establishment of an environment in which the accused's consciousness of guilt can be detected, the purpose of asking defendant to speak was to obtain probative physical evidence and the conduct was merely incident to that effort. [10] [See fn. 10] A guilty party may prefer not to find himself in a situation where consciousness of guilt may be inferred from his conduct, but it can scarcely be contended that the police, who seek evidence from the test itself, will tend to coerce parties into refusing to take tests in order to produce this evidence. [11] Although conduct indicating consciousness of guilt is often described as an "admission by conduct," such nomenclature should not obscure the fact that guilty conduct is not a testimonial statement of guilt. It is therefore not protected by the Fifth Amendment. By acting like a guilty person, a man does not testify to his guilt but merely exposes himself to the drawing of inferences from circumstantial evidence of his state of mind.

We are aware that the United States Supreme Court in Schmerber v. California (1966) 384 U.S. 757, 765, fn. 9 [16 L.Ed.2d 908, 86 S.Ct. 1826], has cautioned that in some cases the administration of tests might result in "testimonial products" proscribed by the privilege. We do not believe, however, that the inferences flowing from guilty conduct are such testimonial products. Rather, the court's concern seemed directed to insuring full protection of the testimonial privilege from even unintended coercive pressures. In the case of a blood test, for example, the court considered the possibility that fear induced by the prospect of having the test administered might itself provide a coercive device to elicit incriminating statements. Such a compelled testimonial product would of course be inadmissible.

Evidence of the refusal is not only probative; its admission operates to induce suspects to cooperate with law enforcement officials. Only the overriding interest in protecting the privilege against compulsory self-incrimination, itself the result of a delicate balance, prohibits evidence or comment in the refusal to testify cases. But the privilege itself is not at issue here. Without exception, none of the reasons that support the privilege lends support to a rule that would exclude probative evidence obtained from an accused's effort to conceal nonprivileged evidence.

[12] In the present case, however, the police officers warned defendant that he had the right to remain silent and that anything he said could be used against him. This warning did not distinguish between speech in terms of communications and speech for voice identification, between a refusal to speak free from sanctions and a refusal to speak productive of detrimental inferences. That distinction would hardly occur to a layman unless it was called to his attention. Thus, defendant's refusal to speak might well have been the direct result of the police warning and cannot be used against him. (Cf. Johnson v. United States (1943) 318 U.S. 189 [87 L.Ed. 704, 63 S.Ct. 549]; People v. Gilbert (1944) 25 Cal.2d 422, 443 [ 154 P.2d 657].)

[13] The usual Fifth Amendment warning that a suspect has a right to remain silent creates this problem, for if taken literally it includes the right not to speak at all. After having given such a warning, if the police direct a defendant to speak for voice identification and he refuses, they must, as a prerequisite to the use of the defendant's refusal to speak as evidence of consciousness of guilt, advise him that the right to remain silent does not include the right to refuse to participate in such a test.

Defendant also assigns as error the prosecutor's repeated references to him and his alibi witness as perjurers. [14] Interpretive, but fair, comment on evidence submitted to the jury is proper. The prosecutor should point out the conflicts and inconsistencies in the evidence and those evidentiary matters that render the prosecution testimony more believable than that submitted by the defense.

Prosecutors tread on dangerous ground, however, when they resort to epithets to drive home the falsity of defense evidence. (See People v. Love (1961) 56 Cal.2d 720, 731 [ 16 Cal.Rptr. 777, 17 Cal.Rptr. 481, 366 P.2d 33, 809].) [15] The term liar, for instance, implies more than offering untrue testimony; it implies a wilful falsehood. (Webster's New Internat. Dict. (2d ed. 1939).) The term perjurer has, as its only formal semantic distinction vis-a-vis liar, the additional element of the oath. (Webster's New Internat. Dict. (2d ed. 1939); see Pen. Code, § 118.) A charge of perjury, however, produces more than moral opprobrium. Perjury is a felony, and the connotation conveyed to the jury is therefore apt to be far more derogatory than that conveyed by the term liar. Particularly when applied to the defendant, it is apt adversely and unnecessarily to affect the ability of the jury dispassionately to weigh the credibility of the accused and the issue of guilt or innocence. [16] Unless the prosecutor is careful to state that his conclusion that perjury was committed is predicated solely on the evidence before the jury, the spectre of jury reliance on prosecutorial access to information outside the record is raised. (See People v. Perez (1962) 58 Cal.2d 229, 246 [ 23 Cal.Rptr. 569, 373 P.2d 617].)

[17] In attacking the credibility of defense witnesses, a single reference to a witness as having perjured himself, based on an analysis of the evidence before the jury, may be unobjectionable. (Cf. People v. Muir (1966) 244 Cal.App.2d 598, 601-602 [ 53 Cal.Rptr. 398].) When, however, as in this case, the prosecutor makes repeated references to defendant and his wife as perjurers, notwithstanding objection, and further makes a suggestion that the issue of perjury bears directly on the issue of guilt, his argument constitutes misconduct. (Cf. People v. Conover (1966) 243 Cal.App.2d 38 [ 52 Cal.Rptr. 172]; People v. Reese (1963) 220 Cal.App.2d 143 [ 33 Cal.Rptr. 561].)

[18] The question remains whether the errors were prejudicial. The evidence presents clearly conflicting stories regarding the crime charged. The victim's identification of defendant was supported by the newsboy, who was unable to identify defendant, but who testified that defendant's car was "similar to the one" he had seen the assailant drive. Defendant and his wife testified that they remained at a bowling alley in Richmond until 4:30 on the morning of the assault, at which time they drove back to Redwood City by way of San Jose. Two independent witnesses, the bowling alley proprietor and his wife, testified to the presence of defendant and his wife at the bowling alley and to their departure at an hour that would have precluded the possibility of defendant's presence at the scene of the crime.

Defendant was identified by three women who testified to five incidents ranging from indecent exposure to use of obscene language in a solicitation to sexual intercourse. None of these incidents involved violence. The first woman's identification was based on a single midnight encounter that had occurred two years earlier. Defendant denied the incident. The second woman testified to being followed in the early morning hours by a man in a car who ran towards her when she parked her car and began walking toward her house. Defendant testified that he was lost that night, was merely attempting to orient himself, and had no evil intent.

The third woman identified defendant and testified to three incidents that occurred after the crime charged and were spaced about two weeks apart. Defendant denied two of the incidents. As to the third incident, which occurred on September 6, 1964, defendant offered an alibi. He testified that both he and his wife were in Sacramento at a bowling tournament on that morning. Defendant's wife and his mother corroborated this alibi. Two disinterested rebuttal witnesses, however, testified that they accompanied defendant to Sacramento and participated in the bowling tournament, that defendant's wife did not make the trip, and that defendant drove back from Sacramento in time to leave the witnesses at a point near the scene of the incident more than an hour before it occurred.

The jury was presented with directly conflicting evidence supported by independent witnesses on both sides. The evidence of consciousness of guilt improperly interjected a factor particularly damaging in a case where the defense is an alibi. The improper argument made the crucial task of objectively weighing the conflicting evidence susceptible to a subjective rejection of the defense evidence. We find, therefore, that it is reasonably probable that a result more favorable to defendant would have been reached absent the errors. ( People v. Watson (1956) 46 Cal.2d 818, 836 [ 299 P.2d 243].)

The judgment is reversed.

Peters, J., Tobriner, J., Burke, J., and Peek, J., concurred.