Horse Auction

A little boy attended a horse auction with his father.
He watched as his father moved from horse to horse, running his hands up and down the horse's legs, rump, and chest.
After a few minutes, little boy asked :
- Dad, why are you doing that ?
His father replied :
- Because when I'm buying horses, I have to make sure that they are healthy and in good shape before I buy.
Johnny, looking worried, said :
- Dad, I think the postman wants to buy Mom.