What's the difference between mens rea and actus reus?

Mens rea and actus reus are two elements of a crime, as it would be explained in court. An academic, Wilson, described mens rea as a "mental attitude" - the psychological element of a crime - e.g. intending to kill someone. This is only relevant to some criminal law, as some 'crimes' are purely regulatory - e.g. serving alcohol to a drunk person - so don't require any knowledge or intent to do that act. Actus reus is sometimes explained as the physical element of a criminal act, for exmaple the act of stabbing someone. An actus reus is usually unspecified, as it's often fairly obvious - the actus reus of polluting a river would be the act of polluting a river - but is sometimes specified for technical purposes (so the courts understand exactly what the charge is).

However, the mens rea may be one of three elements, if it is required at all - it may be knowledge, intent, or recklessness. Intent is defined in cases such as Moloney and