Once upon a time there was a sperm named Stanley who lived inside a famous
 movie actor. Stanley was a very healthy sperm. He'd do push-ups and
 somersaults and limber himself up all the time, while the other sperms just
 lay around on their fat asses not doing a thing.

 One day, one of them became curious enough to ask Stanley why he exercised all
 day. Stanley said, "Look, pal, only one sperm gets a woman pregnant and when
 the right time comes, I am going to be that one."

 A few days later, they all felt themselves getting hotter and hotter, and they
 knew that it was getting to be their time to go. They were released abruptly
 and, sure enough, there was Stanley swimming far ahead of all the others.

 All of a sudden, Stanley stopped, turned around, and began to swim back with
 all his might. "Go back! Go back!" he screamed. "It's a blow job!"