A horsehair worm leaves its home, the body of a mantis. It's an astonishingly long creature. How did it all fit up inside its host?
It's entirely possible that you have a horsehair worm in you, too. Do you feel a slight itching sensation? That could be the worm twisting and churning inside of you.
-via Gizmodo, which also provided the .gif
(OK, actually the worm was curled up inside the insect. It made room for itself by eating the insect's internal organs as it grew.)