To start, scientists isolated the active ingredient in the venom of a species that feeds primarily on worms and opportunistically on fish (Conus tessulatus). The toxic culprit was a particular chain of 27 amino acids that makes the nervous system go haywire, “as though the fish had been hit with a Taser,” the paper reports. When researchers compared this toxin to those in angling species, they saw a striking similarity. Coupled with a reconstruction of the cone snail family tree, the evidence points to the toxin’s emergence before the snails’ ancestors developed a taste for fish. The researchers suggest that venom may have been a defensive adaptation for snails to ward away competition for wiggly worms on the sea floor. When other adaptations arose—such as a harpoon to hold a fish in place—it allowed cone snails to start hunting their new prey.