Fangs on a fish are strange enough, but even weirder is how one toothy group—fang blennies—defends itself from attackers. A new study shows their venom doesn’t inflict pain when tested in mice, unlike the often-excruciating stings of other poisonous fish. Instead, blenny venom causes the victim’s blood pressure to plunge by almost 40% for a short time, which in the wild might slow down a would-be predator (like grouper fish) long enough for the tiny blenny to escape. Even more interesting is how this strange venom—which shares building blocks with the venom of scorpions and cone snails—came to be. When scientists built a blenny family tree using DNA from 11 species, they discovered another surprise: Unlike most venomous animals, which evolve their venom before developing specialized injection tools, the fang blennies evolved their needles before their venom, the researchers report today in Current Biology. After they developed their distinctive enlarged canines, one branch evolved venom glands and turned those teeth into grooved venom-delivery tools (above). The result is possibly the only venomous bite in the animal kingdom that evolved for defense instead of catching a meal.