The mouse
 

Guy walks into the Crown bar with a biscuit tin and a mouse. He says to the barman, watch this:

He sticks the mouse on top of the biscuit tin and it starts dancing.

The barman says. "Blimey, how long does he dance for?"

"As long as you like." Said the guy.

"I’ll give you £50 for it." Says the barman.

"Sold." Said the guy.

That night the guy gets a call from the barman. "How do we stop the mouse dancing, the tapping is driving us mad?"

The guy said. "Lift the lid off the biscuit tin and blow out the candle."