Why does the gas cloud of an underwater gunshot pulse? I have been watching some slow motion video and I was intrigued by the slow motion underwater gunshot.  The first moments of the video go as expected.  The gun fires and a cloud forms in front of the gun.  Then the bullet rips through the water, leaving an open space (which I assume is a cavitation vacuum.)  Soon after, the rip  closes, and the gas bubble shrinks (I'm assuming this is due to the cooling and/or compression of the hot high pressure gasses.)  Then something funny happens.  The bubble pulses a few times and almost appears to emit light.  Each pulse is accompanied by a noise.
The video can be seen here from start, or just showing the bubbles .
What is this pulse effect and/or what causes it?
EDIT: Here is another great video for a possible explanation:
 A: The overall effect (in particular with regard to this light emission, which really happens – it's not just apparent) is mostly investigated under the name sonoluminescence.
Though the process of this luminescence itself remains unsettled, it is for sure that extremely high temperatures are produced at a bubble collapse (in fact, it was conjectured they might be hot enough to build a nuclear fusion reactor!), and this high temperature obviously causes another steam bubble to form very quickly, so that would explain the pulse-oscillation effect.
A: There are many things in nature that lead to periodic phenomena. The governing equation behind all such phenomena with small amplitude is something like $\ddot{x}(t)=-x(t)$. $x$ is the displacement from equilibrium, and $\ddot{x}$ is the acceleration of that parameter. If $x$ is negative, this equation tells us that $x$ is accelerating and trying to become positive. If $x$ is positive, the equation tells us that $x$ is accelerating in the opposite direction trying to become negative. The result is that $x$ oscillates back and forth perfectly between minimum (very negative) and maximum (very positive) values. 
One of the reasons that this effect might seem weird is because we're looking at a gas, not at a liquid. Water is not very springy at all. It takes a lot of force to compress it, and even worse, for each pound of force applied, compressed water barely stores any energy! Gasses are a different story. Think of it this way: If you had a scuba tank pressurized to a certain PSI, you should be much more afraid of a fully pressurized tank of oxygen exploding, than of a fully pressurized tank with 95% liquid water and 5% gaseous oxygen (in different phases, not mixed in). The former stores much more energy than the latter. So, the uncompressed gas is pushed in by the water, the gas builds up a lot of energy in a small space and acts like a spring, then explodes outwards again.
leftroundabout's answer may explain the light emission. On that wikipedia page is a perfectly clear and relevant video: http://en.wikipedia.org/wiki/File:Sonoluminescence_of_Synthetic_Ordnance_Gel.ogv
