A gorilla walks into a bar, and asks for a beer. The barman pours the beer, and the gorilla pays with a crisp new tenner. The barman, thinking gorillas are not too smart, gives change for a fiver, pocketing the rest.

A few minutes later, the barman says to the gorilla "It's funny, but we don't get many gorillas in here" and the gorilla replies "I'm not surprised at the prices you charge!"