A redneck farmer and his wife are lying in bed one evening. The wife is knitting and the husband is reading the latest issue of Animal Husbandry Weekly. He looks up from the page and says to her, "Did you know that humans are the only species in which the female achieves orgasm?"
She looks at him wistfully, smiles, and replies, "Oh yeah? Prove it."
He frowns for a moment and says, "OK," then gets out of bed and leaves the room.
A half hour later the redneck farmer returns, tired and sweaty.
"Well, the cow and the sheep definitely didn't have one. But the way that pig squealed, it's hard to tell!"