The problem is that slugs are not people or animals with higher levels of comprehension or function. The slug reacts to anything that touches its skin, its biggest and most important organ. Its the same thing that makes you pull your finger away from a hot pot even before you feel the pain.
PS: I only froze the slugs and snails to keep them from stinking up my garbage can in the summer. A bag of rotting snails can make a mighty stench, even through a plastic bag.
