boanthropy
(noun)
A psychological disorder in which a human being believes himself to be a bovine.
The most prominent sufferer of the disorder was King Nebuchadnezzar who in the Book of Daniel “was driven from men, and did eat grass as oxen.”
Grandpa Wiggly
Almost 80 and still on the internet. Look out world!
I once suffered from this disorder. I produced vast amounts of salted stick butter.