But getting back to the snail being discussed: it has a very simple map of behaviors.
If wet, seeks light and crawls upwards. If horizontal, it seeks dark. If vertical it crawls up. If upside, it seeks light. When dry, it stops to feed. (Or something like this... I'm going off of memory from 20 years ago.) These very simple behaviors can lead this snail to crawl out of the water along a shore line and eat at the vegetation that exists at the boundary between water and air.
It is quite amazing to see it all reduced to a handful of behaviors which mask lower-level behaviors in a diagram which can be sketched on a cocktail napkin.
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