The Sheep Joke

A farmer buys several sheep, hoping to breed them for wool. After several weeks, he notices that none of the sheep are getting pregnant, and phones a vet for help. The vet tells him that he should try artificial insemination. The farmer doesn't have the slightest idea what this means but, not wanting to display his ignorance, only asks the vet how he will know when the sheep are pregnant. The vet tells him that they will stop standing around and instead will lie down and wallow in grass when they are pregnant. The man hangs up and gives it some thought. He comes to the conclusion that artificial insemination means he has to impregnate the sheep himself.
So, he loads the sheep into his Land Rover, drives them out into the woods, has sex with them all, brings them back, and goes to bed. Next morning, he wakes and looks out at the sheep. Seeing that they are all still standing around, he concludes that the first try didn't work, and loads them in the Land Rover again. He drives them out to the woods, bangs each sheep twice for good measure, brings them back, and goes to bed exhausted. Next morning, he wakes to find the sheep still just standing round. "Try again", he tells himself, and proceeds to load them up, and drive them out to the woods. He spends all day shagging the sheep and upon returning home, falls listlessly into bed.
The next morning, he cannot even raise himself from the bed to look out of the window. He asks his wife to look, and tell him if the sheep are lying in the grass. "No", she says, "they're all in the Land Rover, and one of them is beeping the horn."