The danger is selective. Beneath the anemone's waving arms, a clownfish crosses what should be a firing line, yet its skin does not set off the cnidocytes that arm each tentacle with venom-bearing nematocysts. This is not fearlessness. It is chemistry, negotiated at the body's surface.The old cartoon answer is too tidy: a clownfish simply wears armor. That account fails because the defense is less...More