The pistol and mantis shrimps are both crustaceans that snap their claws and perform magic.
Well, at least a sound and light show: the jet of water squeezed out from between their
claws travels at such speeds that it cavitates - the liquid water under negative pressure
is literally pulled apart into bubbles of water vapor.
When the bubbles collapse in on themselves, they give off a loud "snap," and amazingly,
a small flash of light.
The shrimp use the sonic shock wave to stun or kill prey, but physicists are far more
interested in the flash of light, because we still don't exactly know why it happens.
Collapsing bubbles can also be created in a laboratory simply by using sound - since
sound, as we know, is basically just molecules repeatedly pushing against each other and
then pulling apart, if the sound waves are intense enough, the low pressure will again
be low enough to pull the liquid apart into vapor and cause cavitation bubbles.
The bubbles then collapse, and under certain circumstances, they produce light even brighter
than the shrimp.
This phenomenon of turning sound into light is called "sonoluminescence."
We know that the light flashes are incredibly short - lasting only about 100 picoseconds
- and are surprisingly high energy, meaning the collapsing bubbles may be up to 10 times
hotter than the surface of the sun.
We don't know for sure, though, how the inside of the bubble gets that hot, or what exactly
is giving off the light.
The bubble collapses so quickly that the gases inside are heated by compression, but the
increased pressure might also cause water vapor in the bubble to rapidly condense back
to a liquid, releasing large amounts of latent heat.
And the flash itself might come from glowing red-hot Argon or Xenon gas in the air bubble,
OR from heat tearing water vapor apart into hydroxide and hydrogen ions which then recombine
and give off light, OR from the whole interior of the bubble getting hot enough to become
a glowing plasma - OR it might be a combination.
Either way, the cool thing about sonoluminescence is that it's still not fully understood despite
being fairly simple to create - I mean, you can buy a basic sonoluminescence kit off the
web!
Or just get a pet mantis shrimp.
If you want to hear about more unexplained phenomena in science, a whole bunch of youtubers
like vsauce, veritasium, thebrainscoop, and so forth have made videos about "unanswered
science questions" which you can find listed in the "All Time 10s" video of the same name.