A musician walks into a music shop and says he's interested in buying an accordion. The assistant invites him to look at the range "they're all displayed on the wall over there".

Five minutes later the musician walks up to the assistant with a big grin and says "I'm interested in the big red one".

The assistant says "You're a drummer aren't you".

"Oh, how did you guess?"

"That, sir, is a radiator!"