"'Both the due process clause of the Fourteenth Amendment to the United States Constitution and state law prohibit the state from trying or convicting a criminal defendant while he or she is mentally incompetent. A defendant is incompetent to stand trial if he or she lacks a "'sufficient present ability to consult with his lawyer with a reasonable degree of rational understanding--and . . . a rational as well as factual understanding of the proceedings against him.'" '" (People v. Lewis (2008) 43 Cal.4th 415, 524 (Lewis), quoting People v. Rogers (2006) 39 Cal.4th 826, 846-847 (Rogers); see also 1367, subd. (a) a defendant is mentally incompetent to stand trial if, "as a result of mental disorder or developmental disability, the defendant is unable to understand the nature of the criminal proceedings or to assist counsel in the conduct of a defense in a rational manner".) "A defendant is presumed competent unless it is proved otherwise by a preponderance of the evidence." (People v. Ramos (2004) 34 Cal.4th 494, 507 (Ramos).) However, "'both federal due process and state law require a trial judge to suspend trial proceedings and conduct a competency hearing whenever the court is presented with substantial evidence of incompetence, that is, evidence that raises a reasonable or bona fide doubt concerning the defendant's competence to stand trial. . . . Evidence of incompetence may emanate from several sources, including the defendant's demeanor, irrational behavior, and prior mental evaluations. '" (Lewis, supra, 43 Cal.4th at p. 524, quoting Rogers, supra, 39 Cal.4th at p. 847.) "But to be entitled to a competency hearing, 'a defendant must exhibit more than bizarre . . . behavior, strange words, or a preexisting psychiatric condition that has little bearing on the question of whether the defendant can assist his defense counsel. '" (Lewis, supra, 43 Cal.4th at p. 524, quoting Ramos, supra, 34 Cal.4th at p. 508.) Thus, evidence that "merely raises a suspicion that the defendant lacks present sanity or competence but does not disclose a present inability because of mental illness to participate rationally in the trial is not deemed 'substantial' evidence requiring a competence hearing." (People v. Deere (1985) 41 Cal.3d 353, 358, disapproved on other grounds in People v. Bloom (1989) 48 Cal.3d 1194, 1228, fn. 9.) "'A trial court's decision whether or not to hold a competency hearing is entitled to deference, because the court has the opportunity to observe the defendant during trial.'" (Lewis, supra, 43 Cal.4th at p. 525, quoting Rogers, supra, 39 Cal.4th at p. 847; see also People v. Marshall (1997) 15 Cal.4th 1, 33 (Marshall) "a reviewing court generally gives great deference to a trial court's decision whether to hold a competency hearing," inasmuch as an "appellate court is in no position to appraise a defendant's conduct in the trial court as indicating insanity, a calculated attempt to feign insanity and delay the proceedings, or sheer temper".) "'The failure to declare a doubt and conduct a hearing when there is substantial evidence of incompetence, however, requires reversal of the judgment of conviction. '" (Lewis, supra, 43 Cal.4th at p. 525, quoting Rogers, supra, 39 Cal.4th at p. 847.) Moreover, "when, as here, a competency hearing has already been held and the defendant was found to be competent to stand trial, a trial court is not required to conduct a second competency hearing unless 'it "is presented with a substantial change of circumstances or with new evidence"' that gives rise to a 'serious doubt' about the validity of the competency finding. " (Marshall, supra, 15 Cal.4th at p. 33; see also People v. Lawley (2002) 27 Cal.4th 102, 136.) The trial court may appropriately take into account its own observations in determining whether the defendant's mental state has significantly changed during the course of trial. (Marshall, supra, 15 Cal.4th at p. 33; see also People v. Jones (1991) 53 Cal.3d 1115, 1152-1153 (Jones) the court "need not suspend proceedings to conduct a second competency hearing unless it 'is presented with a substantial change of circumstances or with new evidence' casting a serious doubt on the validity of that finding".)