Scientists from the University of Twente in Enschede, the Netherlands, and their colleagues in Germany have solved the mystery of how snapping shrimp make their distinctive noises. Biologists had theorized that the crustaceans produce the 210-dB snaps, which stun or kill prey and predators, by clamping shut their larger claw. Performing in front of a 40,500-fps video camera, however, the shrimp revealed that they use cavitating bubbles. The researchers describe in the Sept. 22 issue of Science how the 5.5-cm-long shrimp Alpheus heterochaelis produce 100-km/h jets of water with their claw. At this velocity, the jets lower the pressure around microbubbles in their flow to below the vapor pressure of water. The bubbles expand to 7 cm in diameter, then collapse, producing a loud pop 650 µs after the claw has fully closed.