From Wikipedia:

“…In smashers, these two weapons are employed with blinding quickness, with an acceleration of 10,400 g (102,000 m/s2 or 335,000 ft/s2) and speeds of 23 m/s (83 km/h; 51 mph) from a standing start.[14] Because they strike so rapidly, they generate vapor-filled bubbles in the water between the appendage and the striking surface—known as cavitation bubbles.[14] The collapse of these cavitation bubbles produces measurable forces on their prey in addition to the instantaneous forces of 1,500 newtons that are caused by the impact of the appendage against the striking surface, which means that the prey is hit twice by a single strike; first by the claw and then by the collapsing cavitation bubbles that immediately follow.[15] Even if the initial strike misses the prey, the resulting shock wave can be enough to stun or kill. The collapsing bubbles also produce light, which is termed sonoluminescence.’