<P> For conduct to constitute an actus reus, it must be engaged in voluntarily . Few sources enumerate the entirety of what constitutes voluntary and involuntary conduct . Oliver Wendell Holmes, in his 1881 book The Common Law, disputed whether such a thing as an involuntary act exists: "(a) spasm is not an act . The contraction of the muscles must be willed ." A few sources, such as the Model Penal Code, provide a more thorough treatment of involuntary conduct: </P> <Ol> <Li> a reflex or convulsion; </Li> <Li> a bodily movement during unconsciousness or sleep; </Li> <Li> conduct during hypnosis or resulting from hypnotic suggestion; </Li> <Li> a bodily movement that otherwise is not a product of the effort or the determination of the actor, either conscious or habitual . </Li> </Ol> <Li> a reflex or convulsion; </Li> <Li> a bodily movement during unconsciousness or sleep; </Li>

Which of the following is necessary for a criminal act to be considered an actus reus