@gnaddrig It's easy: snails and slugs don't have any "seal" on their foot. (Trying too hard to understand slop can distract the brain from more important things.) But land snails can close their aperture, the opening of their shell, with a very thick, hardening slime. It's a protection against dehydration, cold, and enemies: https://www.nhm.ac.uk/discover/snails-and-slugs.html In spring, after a drought, they eat it from inside and come out again. If you see snails with such a plug: they are not dead, only protected. 1/2