Snakes.

Having arrived at the edge of the river, the fisherman soon
realized he had forgotten to bring any bait. Just then he
happened to see a little snake passing by who had caught a
worm. The fisherman snatched up the snake and robbed him of
his worm. Feeling sorry for the little snake with no lunch,
he snatched him up again and poured a little beer down his
throat and went about his fishing.

An hour or so later the fisherman felt a tug at his pant
leg. Looking down, he saw the same snake with three
more worms.