Boanthropy is a psychological disorder in which a human believes himself or herself to be a bovine.

The most famous sufferer of this disorder is claimed to be Nebuchadnezzar II, who in the Book of Daniel "was driven from men, and did eat grass as oxen". Most probably, the authors were making fun of his aversion to meat or violence.

Carl Jung would subsequently instance 'Nebuchadnezzar...[as] a complete regressive degeneration of a man who has overreached himself'.

According to Persian traditions, the Buyid prince Majd al-Dawla was suffering from an illusion that he is a cow, making the sound of a cow and asking that to be killed so that his flesh could be consumed. He was cured by Avicenna.