Two blondes were roofing a house. One would pull out a nail and then
hammer it into the roof. Then he would pull out another nail, look
at it, then throw it over his shoulder. Blonde two eventually saw what
blonde one was doing, watched him a while and then said, "Why do you keep
throwing out every other nail?". The first blonde replied, "Because their
point is on the wrong end." The second blonde then said, "You airhead,
those nails are for the other side of the roof!"