The actus reus is the physical element of a crime. It can be an act, a failure to act, a state of affairs. For some crimes the act or omission must also result in a consequence. The act or omission must be voluntary on the part of the defendant. An act picking up an item in a shop; or punching a victim which could be part of the physical element of an assault occasioning actual bodily harm. An omission failing to provide a specimen of breath; or wilful neglect of a child. For common law crimes an omission is only sufficient for the actus reus where there is a duty to act. This can be a contractual duty; in Pittwood a railway crossing keeper omitted to shut the gates so that a person crossing the line was struck and killed by a train. The keeper was guilty of manslaughter.