So I'm sitting in a bar, working my way through a bottle of beer, when this guy sits down next to me. Middle-aged, maybe fifty-ish, buzz-cut, glasses, looks ex-military. Eh. Seen people like this all over the place; I don't think anything of it.
He orders a beer, take a swig, then out of nowhere tells me, "I'll bet you twenty bucks I can't bite my right eye."
Mind you, this was back in my early 20s. I was still really naive. I hadn't yet learned the maxim of "if someone bets you they can't do something, they can". So I'm thinking, That's ridiculous. No one can bite their eye. And I've got money to burn, so I accept.
This guy takes his glasses off, pops out his false eye, then proceeds to put it between his teeth.
I'm mentally kicking myself while I get out my wallet. He's still putting the glass eye back in place, and says he'll make it double-or-nothing that he can't bite his left eye.
Now, no one has two glass eyes. And I still haven't learned my lesson. You're on, says I.
What's he do? He takes out his false teeth, and gently presses them into his (still real) left eyeball.