The title is pretty misleading. Paradoxum doesn't effect the snail's brain or behavior directly. It doesn't compel them to stand out in the open; it just renders the snail blind to light sources. Snails have very simple light-detecting eyes, and seek shade to hide from predators. But this parasite in its eyestalks makes it more difficult for a snail to detect light, so they stay out in the open more often than a non-infected snail and end up getting eaten by birds attracted to the pulsing colors.
Sometimes just their eyestalks will be torn off, and will regenerate with more Paradoxum growing inside it, so the parasite can infect multiple birds throughout its life!