The snapping shrimp has one claw far bigger than the other, and when it shuts it, one of the loudest sounds on a reef goes off. For a long time people assumed the noise was the claw itself, two hard halves slamming together. In 2000 a team in the Netherlands filmed the snap at high speed with a hydrophone beside it and found the sound arrives a beat too late for that. Closing the claw throws out a jet of water so fast it tears a bubble open in the sea, and the bang is the bubble caving in. A year later they caught that collapse giving off a flash of light, from a bubble whose inside had reached at least five thousand kelvin. So the shrimp’s famous weapon is not really the claw. It is the brief hole the claw makes in the water, and what happens when the sea fills it back in.