The physics of the pop
In the coral reefs of the Caribbean, a creature measuring only 3-5 centimeters long produces one of the loudest sounds in the ocean. Members of the Alpheidae family, commonly known as pistol or snapping shrimp, possess one oversized claw that is a high-speed weapon. This claw, which can be larger than half the shrimp's body, has a two-part structure. A mobile "hammer" section pulls back and locks into place, and when released, it snaps shut with incredible speed.
The resulting motion fires a jet of water at speeds up to 100 kilometers per hour (about 62 mph). This rapid water movement is governed by Bernoulli's principle; the high velocity causes the local pressure to drop dramatically, forming a low-pressure vapor-filled bubble in the water. This process is known as cavitation. The entire event, from the claw snap to the bubble's collapse, occurs in under a millisecond. The sound itself doesn't come from the two parts of the claw hitting each other, but from the violent collapse of this cavitation bubble.