A man camped in a national park, and noticed Mr.

A man camped in a national park, and noticed Mr. Snake and Mrs. Snake
slithering by. "Where are all the little snakes?" he asked. Mr.
Snake replied, "We are adders, so we cannot multiply."

The following year, the man returned to the same camping spot. This
time there were a whole batch of little snakes. "I thought you said
you could not multiply," he said to Mr. Snake. "Well, the park ranger
came by and built a log table, so now we can multiply by adding!"