Amy, a city girl, marries a farmer. One morning, before he goes out to the fields, the farmer says to her, "The artificial insemination man is coming today to impregnate one of our cows. I drove a big nail into the two-by-four over the cow's stall. You show him where it is."
The farmer leaves, and a bit later, the artificial insemination man arrives. Amy takes him down the rows of cows until she sees the nail.
She tells the man, "This is the one, right here."
He asks her, "How do you know?"
Amy says, "By the nail over its stall."
The man asks again, "What's the nail for?"
Amy says, "I guess it's to hang your pants on."
