African Carpenter

A carpenter is busy nailing planks onto a wooden house. One hand holds a bunch of nails. Every now and then he throws a nail over his shoulder, and then continues banging away.
The foreman sees this. “Hey you! Why are you throwing nails away!” he shouts.
The carpenter replies: “Their heads are on the wrong side!”
“You idiot!” the foreman shouts back. “Those are for the other side of the house!!”