What is the test for a jury to determine whether a defendant committed an intentional act or an intentional failure to do a required act?

It is unclear from the record whether the prosecution's theory of the case was premised on an intentional act or an intentional failure to actthe prosecutor argued both that the defendant committed an intentional act by keeping the dogs when he knew the dogs were dangerous and were getting out and attacking passersby and that the defendant knew his dogs were dangerous and failed to "get rid of the dogs or keep the dogs safely confined." The addition of the phrase "or failed to do a required act" to the CALCRIM No. 520 instruction, reflects a trail court determination that a legal duty was requisite to its theory. The instruction would have been more complete had the court explicitly instructed the jury on the legal duty appellant owed the victim, but if the failure to do so was error, as appellant contends, we are satisfied that the error was harmless under the People v. Watson standard. (People v. Watson (1956) 46 Cal.2d 818, 836 (Watson).)

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"When a criminal statute does not set forth a legal duty to act by its express terms, liability for a failure to act must be premised on the existence of a duty found elsewhere. [Citation.]" (Heitzman, supra, 9 Cal.4th at p. 198.) A criminal statute may incorporate a duty imposed by another criminal or civil statute, and "may also embody a common law duty." (Ibid.) This court explained in People v. Rolon (2008) 160 Cal.App.4th 1206, 1216, "[t]o recognize that a criminal statute may embody a common law duty to act, as Heitzman does, is not to impose criminal liability without a statute. The statute is still the source of liability; the common law only provides the rationale that failure to act can be equivalent to an affirmative act in some situations."