Sam takes one end and starts hammering with some nails. He takes a nail, hammers it in, takes another nail and throws it away. Again he hammers a nail in and throws the next one away. This ritual continues for some time. When Hank notices what Sam is doing, he asks, "Why the hell are you throwing away those nails?"
Sam replies, "The ones I discarded were all pointed on the wrong end."
Hanks is irritated and says, "You dumbo, those were meant for the other side of the garage!"