A man walks into a bar with a metal box under one arm and a duck under the other.

The man walks up to the bar and asks the bar tender
"if you give me a free bottle of beer I'll show you my dancing duck".

The barman is surprised, but gives the guy a Bud and asks the bloke to show him the duck dancing. So the guy puts the metal box on the bar, and stands the duck on top of it. A few seconds later the duck starts to jump around, as if he's doing an Irish jig.

Everyone in the bar is now watching this duck dancing, and the barman offers the guy $50 for the duck and the box. The bloke accepts, and the pub is filled day and night for 3 days with people watching the amazing dancing duck.

So 3 days after he sold the barman the duck, the guy walks back in to the pub and sees his duck dancing on the box on top of the bar.

The barman sees the guy and offers him a bottle of Bud on the house.
As he gives the guy the Bud, the barman asks,
"Could you tell me how you stop the duck from dancing on top of the box?"

The man replies, "Oh that's easy, you just take the hot coals out."