Sam the Sperm...
Once long ago there was a sperm named Sam who lived inside the testicles of a famous rock star. Sam was always a very healthy and strong sperm, he'd spend his time doing exercises and somersaults, while all the other sperm just laid around waiting for their eventual release.
One day one of the other sperm got curious and asked Sam why he always worked out, and Sam said
"Look my friend only one of us can fertilize a woman's egg and grow into a human baby, and when that time comes, I am going to be the one who gets there first."
A few days later all the sperm felt the temperature getting hotter and hotter and they knew their time had come. They all waited and suddenly their was a release, and sure enough there was Sam swimming far ahead of the others.
All of a sudden Sam put on the brakes, turned around, and started swimming back with all his might.
"GO BACK! GO BACK!" he screamed... "It's a blow job!"
