I'm thinking that the radiative energy is lost and the molecular kinetics are held by the impermeable barrier. This explains the powder because as the prince rupert cools, the ouside holds its shape creating an artificial volume. the interior's pressure is likely a gradient to vacuum, and once the surface of the object is broken, it allows the latent vibration of molecules to shake themselves to pieces as they "cool" to normal size.

Awesome video and channel!

It took moment for me to realize that the bubble must also be a vacuum. With regard to wondering why there are no shards: I am far from an expert in this, but due to the intense though equal pressures in all directions, the result of the breaking glass are particles that are as near to round as they can be, though as a crystalline substance (I have no direct experience with this stuff) would appear more like sand or powder. Doesn't the equalization of pressures when the tail is broken also mean that the glass to some invisible degree (may need special equipment and cameras) shrinks/contracts? It may also be that when forces are a lot less equal is why shards would be created in broken glass, though I cannot guess exactly why the fractures necessarily choose their paths as they do. Light bulbs spring to mind as being similar but they are not vacuums since they are filled with a gas which enhances the glowing filament and they are manufactured somewhat differently I believe.

so many books :O

Like, I mean, I don't know a lot about these things but I would imagine that the force is so huge that it will turn any big piece of glass into shreds, so you end up with only the tiny sand-like structures sticking around. And maybe bigger glass pieces end up with bigger stress differentials, or something of that sort, and want to break up with pieces of roughly uniform stress?... I'd imagine you'd have to take concepts from physics, chemistry, and material science to fully understand this. Again, I don't really know. My intuition was shouting "it must feel like sand" at that point in the video, since safety glass is made the way a prince rupert's drop is... But why safety glass doesn't break into shreds that can cut you is another question...

you need to run the audio though a denoising app...