Some cone snails have venom strong enough to kill humans, though they prefer using it on their prey.
The genes that produce the toxins have evolved amazingly fast. Predatory marine snails that kill their prey with a toxin so poisonous it can be fatal to humans may have the fastest evolving genes in the world. Toxic Conus uses a poisonous harpoon to capture its prey. The snail will kind of sneak up on a fish, inject the venom, and the fish immediately goes under paralysis and kinda falls on its side. Most cone snails are harmless but there is a relatively large group belonging to the genus Conus that secretes venom.