One morning, on his way out to check on the cows, the rancher says to Amy,
'The insemination man is coming over to impregnate one of our cows today.
I drove a nail into the 2 by 4 just above the cow's stall in the barn. You show him where the cow is when he gets here, okay?'
The rancher leaves for the fields. After a while, the artificial insemination man arrives and knocks on the front door. Amy 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.'
The man, assuming he is dealing with an air head blonde, asks, 'Tell me lady, 'cause I'm dying to know; how would YOU know this is the cow to be bred?'
'That's simple. By the nail over its stall,' Amy explains very confidently...
Laughing rudely at her, the man says, 'And what, pray tell, is the nail for?'