User blog comment:Pacifista15/Explosive Punches/@comment-152.17.124.40-20111031143312

This reminds me of the "cavitation" effect.

The cavitation effect appears when things in water move so fast that the leave a bubble of nothing, a vacuum bubble. This bubble then collapses, releasing a powerful sound/pressure shockwave and very high temperatures (in a localized environment, normally). This CAN be created by animals in our world, so Luffy being able to do it on a larger scale isn't unbelievable. Both the Mantis shrimp and the Pistol shrimp use the cavitation effect to take down prey.

What makes me doubt that it IS the cavitation effect is that if Luffy is using that, then Red Hawk would only work underwater, which he can't expect to be fighting in much.

(obligatory wikipedia citation: http://en.wikipedia.org/wiki/Alpheidae#Snapping_effect )