From barnacles that hijack crabs to a protozoan that makes rodents cozy up to cats, parasites do a lot more than make you puke. But for sheer gross-out glory, it’s hard to beat Leucochloridium paradoxum. These flatworms live in birds’ rectums, and they give garden snails a glimpse of hell.

1/ A grazing snail eats a bird dropping. Gross, right? Well, what’s even grosser is that the dropping is filled with parasite eggs. Garden snails can’t digest the eggs. They survive their trip through the snail’s tummy intact and spread to nearby organs.

2/ The invading Leucochloridium runs through a couple of life-cycle stages before landing in the snail’s hepatopancreas, the organ that passes for its liver-pancreas-thing.

3/ The parasite pumps embryo after embryo into fat, throbbing brood sacs it builds in the snail’s eyestalks.

4/ An intelligent designer might have stopped at systemic infection and pulsating, brightly colored tentacles. Not evolution, though. Evolution goes up to 11. The parasite takes control of the snail’s rudimentary brain, making the mollusk forget that it’s scared of daylight and spurring it to inch out into the open.

5/ To us, the infected tentacles look like a fleshy, Cronenbergian nightmare. To birds, they look like delicious caterpillars.

6/ The birds eat the eyestalks and get infected by the parasites, which reproduce and lay eggs in the bird’s rectum, ready to be deployed in future poop.

7/ Even if the snails survive the destalking, they stay parasitized—which means they can infect other birds, which can infect other snails. It’s the circle of life.