In 1950, a Melbourne woman named Mrs. Patricia Cogdon struck her daughter Pat twice on the head with an axe while deeply asleep, killing her instantly. Cogdon had been dreaming that Korean War soldiers were attacking her daughter and that she was defending her with a spider-hunting weapon.
When brought to trial for murder, her legal counsel presented the defense of non-insane automatism. Under common law, criminal liability requires both actus reus (a guilty act) and mens rea (a guilty mind). Furthermore, for an act to constitute actus reus, it must be voluntary.
Medical experts testified that Mrs. Cogdon was experiencing an episode of somnambulism (sleepwalking) brought on by extreme stress, leaving her conscious mind completely unattached to her physical movements. Because her actions were entirely involuntary, she lacked the capacity for voluntary action altogether.
The jury returned a verdict of not guilty, cementing non-insane automatism as a rare but potent defense in criminal law where involuntary physical spasms or somnambulistic states nullify actus reus.