Two blondes are building a toolshed

Two blondes are building a toolshed

One of them is trying to hammer a nail into one of the walls, but she's holding the nail backwards--the head of the nail against the wall, striking the tail with the hammer. She complains that the nail isn't going in. Her companion says, "Idiot! See how the nail is facing the other way? It's supposed to go into the opposite wall!"