Two drunks stumble out of a bar, deciding to go home. While they are walking down the road, they discuss which colour the moon has. The first says it's green, the other says it's blue. So they decide to ask a bobby if they cross one's way.
After a quarter hour of stumbling around in the dark streets they find one and ask "Which colour has the moon up there?"
And the police officer answered "Which moon - the left one or the right one?"