Whenever I give a talk about my book Parasite Rex,Parasite Rex, I try to gather together the creepiest images of parasites that I can. Every time, there’s one kind of parasite that summons an instant reaction: a mix of laughter, sucked-in breaths, and gasps of recognition. I speak, of course, of the parasites that eat your tongue.

I only mean you if you’re a fish. Some species of isopods (crustaceans related to the less creepy crabs and lobsters) will swim into the gill of a fish, make their way to its mouth, and devour its tongue. It will jam its legs into the gills to hold itself in place, facing forward, its eyes gazing out of the fish’s mouth,