The Musical Octopus
The man walks into a bar with his octopus. He sits the octopus down on a stool and tells everyone in the bar that this is a very talented octopus and "He can play any musical instrument in the world." Everyone in the bar laughs at the man and generally reckon he's an idiot. At that the guy announces that he will wager £50 to anyone that the octupus can play any instrument that they care to provide.
Immediately a challenger walks up with a guitar and sets it beside the octopus who picks it up and starts playing better than Jimi Hendrix. In amazement the guitar man pays