A donkey walks into a bar. "I'll have a pound" he says to the barman. The barman says " You mean a beer"? "No" says the donkey "I mean a pound". The barman opens the till and takes out a coin and holds it up "This is a pound" he says "A beer costs a pound". The donkey looks quizzical "That's a pound? Let me have a look". He takes the coin and turns it over slowly "So this is a pound"? "Yes" says the barman patiently. "In that case I'll have a beer" says the donkey "I seem to have the right money".