Recursion
A child couldn't sleep, so her mother told her a story about a little frog, who couldn't sleep, so the frog's mother told her a story about a little bear, who couldn't sleep, so the bear's mother told her a story about a little weasel... who fell asleep. ...and the little bear fell asleep; ...and the little frog fell asleep; ...and the child fell asleep.
See also: Recursion and self-reference.