I bet I can bite both of my eyes

A man walks into a bar has a few drinks and asks what his tab was. The bartender replies that it is twenty dollars plus tip. The guy says, "I'll bet you my tab double or nothing that I can bite my eye." The bartender accepts the bet, and the guy pulls out his glass eye and bites it.

He has a few more drinks and asks for his bill again. The bartender reports that his bill now is thirty dollars plus tip. He bets the bartender he can bite his other eye. The bartender accepts knowing the man can't possibly have two glass eyes. The guy then proceeds by taking out his false teeth and biting his other eye.