Buying a Horse_英语笑话

lil' johnny attended a horse auction with his father. he watched as his father moved from horse to horse, running his hands up and down the horses' legs, rump, and chest.
after a few minutes, johnny asked, "pop, why are you doing that?"
"because i'm thinking of buying these horses."
johnny looked worried, "then i think we'd better hurry home right away!"
"why?" his father asked.
"because the ups man stopped by yesterday, and i think he wants to buy mom!"