There was a sperm that decided he would get in good shape so he could beat the other sperms to the egg and fertilize it. He exercised and was in great shape when the call finally came and he took off and was far ahead of the other sperms, he would get to fertilize the egg. Suddenly he came rushing back the way he'd come yelling go back, go back -blow job, blow job.
You remember the Woody Allen movie, "Everything you wanted to know about sex but were afraid to ask" parody of the book? The last scit in the movie was them all lined up as sperm in white helmets + garb in a parachute mode + the old old grizzled sargeant looks at Woody Allen + asks, "1st jump kid?"