It should be fairly easy to spot a patient suffering from boanthropy. He or she may well be down on all fours chewing grass. Boanthropy is a psychological disorder in which the sufferer believes he or she is a cow or ox.

The most famous sufferer of this condition was King Nebuchadnezzar, who in the Book of Daniel “was driven from men and did eat grass as oxen”. Nebuchadnezzar was the king of the Neo-Babylonian Empire from 605BC to 562BC. According to the Bible, he conquered Judah and Jerusalem and sent the Jews into exile. He was also credited with building the Hanging Gardens of Babylon.

Nebuchadnezzar was humbled by God for boasting about his achievements, lost his sanity and lived like an animal for seven years, according to Daniel, chapter 4. When his sanity was later restored he praised and honoured God.

Aside from boanthropy, other explanations for his behaviour include porphyria (a group of enzyme disorders that manifest with neurological symptoms including hallucinations, depression, anxiety and paranoia) or general paresis or paralytic dementia caused by syphilis.

The porphyrias are a group of rare inherited or acquired disorders of certain enzymes that normally participate in the production of porphyrins and haem. They manifest with either neurological complications or skin problems, or occasionally both.

The metamorphosis of humans into animals is known as therianthropy, the best known form of which is lycanthropy — transformation into a wolf or werewolf. The term “cynanthropy” dates back to ancient Greece and is applied to shapeshifters who alternate between human and dog form.

A therianthrope, however, is a being that is part human, part animal. The best known examples are the animal-headed gods of ancient Egypt, such as Bast (with the head of a cat) or Anubis (with the head of a jackal). The word combines the Greek therion, wild animal, with anthropos, human being.