One day, a farmer was tending to his livestock when he noticed that one of his cows was completely cross-eyed. He called up a veterinarian friend of his who told him to bring in his cow. The vet took one look at the cow, stuck a tube up the cow's butt, and blew into the tube until the cow's eyes straightened out. The vet charged the farmer a hundred bucks, and the farmer went home happy.
About a week later, the cow's eyes were cross-eyed again, but this time the farmer figured he could probably take care of it himself. So he called his hired hand over, and together they put a tube up the cow's butt. The farmer put his lips to the tube and started to blow. Strangely, nothing happened, so he asked his hired hand to give it a try. The hired hand removed the tube, turned it around, put it in the cow's butt and started to blow.
"What are you doing?" asked the farmer, horrified.
"Well, I wasn't gonna use the side that YOU had put your lips on."