Shrimp CavitateThose of us who left active duty before the year 2000 probably missed this sonar tidbit. Although the concept sounds goofy, it is supported well enough in scientific communities to assure winning your next beer bet.
From the start of WWII, researchers studied snapping shrimp. As any submariner knows and many heard firsthand, these "biologicals" create loud, underwater noise. Colonies produce such a din that during World War II, the constant crackling from these shrimp sometimes foiled the military's attempts to find enemy subs.
For years, the assumption had been that the cracking sound occured when the moving part of the shrimp's claw struck its stationary opposite, like castanets. Instead, cavitation--the mechanical process which plagues ships' propellers--is to blame. Cavitation occurs when liquid is forced to move above a certain speed and, as a result, experiences a pressure drop (known as Bernoulli's principle). This phenomenon causes tiny air bubbles in the fluid to swell. As the fluid slows and the pressure again rises, the imploding bubbles generate a shock wave with audible sound.
The little ol' shrimp communicate with one another, defend their territory, and stun their prey with this sound.
For doubters: here, here and you more scientific folk will like the link here.