Answer:
When you pour salt on a snail/slug the water is very quickly pulled out of the cells of the snail's body by a process called osmosis. As it dries out, the snail's body produces a slimy substance to protect itself. The bubbling comes from the slime and air being forced out of the snail's body as it shrivels up. If enough salt is poured on the snail it will die of dehydration very quickly.