Zombie Snails (2:40)

When a snail eats these parasites the parasites take over the snails tentacles and brain to ensure that the parasite's offspring lives on. The snail becomes food for a bird, and the cycle continues when another snail eats the bird droppings.

http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/deadliest-zombie-snails/?source=vidcarousel