Let’s Get Crazy
For centuries, doctors associated insanity and other medical afflictions with lunar cycles, hence the terms “lunatic” and “lunacy” to describe an affected person.
Since most nuts, like the human head, are hard with valuable contents, people have used “nut” as slang for “head” since at least the mid-1800s. The term “off his nut” described someone who seemed separated from his head and senses, and this was later shortened to just “nuts.”
An unpredictable and dangerous person is sometimes called a “loose cannon.” Early cannons of the wooden ship days were not yet secured in fixed spots, but were wheel-mounted and could be rolled to different gunports on the ship. When one of these extremely heavy guns broke loose on deck during high waves or battle, the “loose cannon” was a clear danger to nearby crewmen, often causing gruesome and fatal injuries.
The word “demented” comes the Latin “dementare” or “out of one’s mind.”
If you’ve ever described someone as “going berserk,” you were invoking the name of ancient Norse warriors known for fighting with wild fervor and other acts of brutality. Berserker translates to “bearskin,” as animal skins were often part of the warriors’ attire, which was thought to contribute to the European werewolf legends.
Many ancient civilizations considered insanity to be caused by possession by evil spirits or demons, as did many religions. For example, Jesus casts devils and demons out of the afflicted in several Bible passages.
Cuckoo birds are likely considered “crazy,” because of their repetitive, incessant calls and habit of placing their own eggs in the nests of other birds. By some accounts, male cuckoos are crazy for tolerating their partner’s infidelity and outsourcing of childrearing, and the polyandrous female is crazy because she “fools around.”
Palmatier, Robert Allen, Speaking of Animals: A Dictionary of Animal Metaphors, Greenwood Press, 1995 (page 105)