A guy walks into a bar and orders a beer.

After he is served the beer he asks the guy next to him to watch his drink while he uses the bathroom. He does his business, and when he returns the guy watching the drink says “I wouldn’t drink that if I were you.” “Why not?” He asks. “That monkey over there, came over and peed in it” he informs him. “What,” says the man, “whose monkey is that!?” “I think it’s the piano player’s monkey,” the other guy tells him. The man goes up to the piano player and says, “hey, do you know your monkey peed in my beer?” The pianist replies, “no, but if you hum it I’ll try to play it.”