~43 years ago he bit the head off a bat accidently: https://www.rollingstone.com/music/music-news/ozzy-osbourne-...

I'm not sure how that turned into "he’s bitten the heads off of various animals"

"That night in Des Moines, someone threw a live bat. “I thought it was a rubber bat,” Osbourne said. “I picked it up, put it in my mouth, crunched down, bit into it, being the clown that I am.”"