This is an *old* story. I most recently saw it posted on alt.Callahans by PunsterGal.

There once was a snake farmer who had a pair of snakes he was trying to breed. For the life of him, he couldn’t get them within two feet of each other. Frustrated, he called up the local herpetologist, and explained the situation.

She hurried over, picked up the snakes, and looked at them. “You know what I would do?” she said. “See that tree over there? Chop it down, chop off a good sized log, split the log in two, and made two tables out of them. Put the table and snakes into a cage, and leave them alone for a while.” Well, the breeder thought this was insane, but having no other options, he tried it. Sure enough, a few days later, he had a whole slew of baby snakes. He called up the expert, and asked her how that was possible.

She replied, “Well, you see, your snakes are adders, and everybody knows that adders can multiply only on log tables.”