Amy, a blonde Texas girl marries a Texas rancher. One day, the rancher tells Amy that the artificial insemination man is coming today to impregnate one of their cows. He tells Amy that he drove a nail into the two by four just above the stall of the cow to be impregnated. He tells her to just show him which cow when he gets there. So off goes the rancher to do his chores. When the artificial insemination man arrives later, Amy takes him to the barn. They are walking along the long row of cows and when she spots the nail she tells him this is the cow.
The man is impressed by what he thought was going to be another dumb blonde. He asks, "How did you know which cow was to be bred?" She said, "Simple, by the nail over the stall." The man asks, "What's the nail for?" She says, "I guess it's to hang your pants on.":