What constitutes heat of passion in a murder case?

"Murder is the unlawful killing of a human being . . . with malice aforethought." ( 187, subd. (a).) "A killing with express malice formed willfully, deliberately, and with premeditation constitutes first degree murder. [Citation.] 'Second degree murder is the unlawful killing of a human being with malice aforethought but without the additional elements, such as willfulness, premeditation, and deliberation, that would support a conviction of first degree murder.' [Citation.]" (People v. Beltran (2013) 56 Cal.4th 935, 942.) "A person who kills without malice does not commit murder. Heat of passion is a mental state that precludes the formation of malice and reduces an unlawful killing from murder to manslaughter. Heat of passion arises if, ' "at the time of the killing, the reason of the accused was obscured or disturbed by passion to such an extent as would cause the ordinarily reasonable person of average disposition to act rashly and without

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deliberation and reflection, and from such passion rather than from judgment." ' " (Ibid., fn. omitted.)

A trial court has the duty "to instruct fully on all lesser necessarily included offenses supported by the evidence." (People v. Breverman (1998) 19 Cal.4th 142, 148-149.) We need not determine whether the trial court erred in failing to instruct the jury that provocation in the form of a sudden quarrel or heat of passion may reduce murder to manslaughter because any error was harmless under any standard.