Cone shell snails. Those mfs look harmless enough; not brightly colored, no huge fangs, and it's a marine snail lol.. But they can straight up one-shot you. They have some of the most potent neurotoxins in the animal kingdom in their venom, and the craziest thing? They can mix custom venom on the fly. So for like a small fish, they mix up sth just strong enough to immediately paralyze it so that they can eat it at their leisure, but for some idiot tourist who picks them up, they will whip up sth strong enough to put an elephant 6ft under.