A retired psychology professor passed this "olde" humor on to me....
The floods had subsided, and Noah had safely landed his ark on Mount Sinai. "Go forth and multiply!" he told the animals, and so off they went two by two, and within a few weeks Noah heard the chatter of tiny monkeys, the snarl of tiny tigers and the stomp of baby elephants.
Then he heard something he didn't recognise… a loud, revving buzz coming from the woods. He went in to find out what strange animal's offspring was making this noise, and discovered a pair of snakes wielding a chainsaw. "What on earth are you doing?" he cried. "You're destroying the trees!"
"Well Noah," the snakes replied, "we tried to multiply as you bade us, but we're adders… so we have to use logs."