Carol, a blonde city girl, marries a dairy farmer.

One morning, on his way out to check on the cows, farmer John says to Carol 'The insemination man is coming over to impregnate one of our cows today. I drove a nail into the rail above the cow's stall in the barn. You show him where the cow is when he gets here, OK?'

So then the farmer leaves for the fields.

After a while, the insemination man arrives and knocks on the front door. Carol takes him down to the barn. They walk along the row of cows and when she sees the nail, she tells him 'This is the one...right here.'

Terribly impressed by what he seemed to think just might be another dizzy blonde, the man asks

'Tell me lady, how did you know this is the cow to be bred?'

'That's simple; by the nail over its stall', Carol explains very confidently.

Then the man asks, 'What's the nail for?'

She turns and starts to walk away and with complete confidence, says over her shoulder ......

I assume it's to hang your trousers on!