Amy, a blonde city girl, marries a rural rancher. One morning, on
his way out to check on the cows, the rancher says to Amy, 'The
artificial insemination man is coming over to impregnate one of our cows
today. I drove a nail into the two-by-four just above the cow's stall in
the barn. You show him where the cow is when he gets here, okay?'

After a while the artificial insemination man arrives and knocks on the
front door. Amy takes him down to the barn. They walk past cow after
cow and when she finally sees the nail, she tells him, 'This is the one.... right here.'

Terribly impressed by what he thought just might be another dumb blonde,
the man asks, 'Tell me little lady, how did you know this is the cow to
be bred?'

'That's simple: By the nail over its stall,' Amy says.
Then the man asks, 'What's the nail for?'

She turns to walk away, and with complete confidence says, 'I guess it's to hang your pants on.'