That’s not exactly what’s happening? The snails aren’t dead (which is kind of a requirement for being a zombie) and their brains have not been “hijacked” (because snails don’t have brains). The video in the link describes the parasite as having ‘hypnotized the snail into walking into the sunlight,’ which is by itself pretty misleading. The presence of the parasite makes the snails less sensitive to light, so they simply do not know where they are safe and where they aren’t. This is certainly to the parasite’s advantage, because their life cycle continues in the guts of birds.
A parasite that inflates the snails’ eyestalks with its broodlings so the stalks look like delicious, squirmy maggots is disturbing enough, I think. They’re called leucochloridium paradoxum.
If you’re wondering how we find writers for SciShow…it’s seeing posts like this on Tumblr.