What is the test for disqualifying a mentally ill or delusional witness?

verdict. To warrant the rejection by a reviewing court of statements given by a witness who has been believed by the trial court or the jury, there must exist either a physical impossibility that they are true, or it must be such as to shock the moral sense of the court; it must be inherently improbable and such inherent improbability must plainly appear. [Citations.]' " (People v. Breault (1990) 223 Cal.App.3d 125, 140-141; see People v. Young (2005) 34 Cal.4th 1149, 1181.)

A person may be disqualified as a witness only if he or she is "(1) Incapable of expressing himself or herself concerning the matter so as to be understood, either directly or through interpretation by one who can understand him; or [] (2) Incapable of understanding the duty of a witness to tell the truth." (Evid. Code, 701, subd. (a); see Evid. Code, 700; People v. Mincey (1992) 2 Cal.4th 408, 444.) Even mentally ill and delusional witnesses are qualified to testify, and it was up to the jury (and the trial court, in ruling on the motion for new trial) to decide how much of Pavao's testimony should be credited. (See Lewis, supra, 26 Cal.4th at pp. 357-358 [although testimony "may have consisted of inconsistencies, incoherent responses, and possible hallucinations, delusions and confabulations, [the witness] 'presented a plausible account of the circumstances of [the victim's] murder' "].)