Slow motion video is pretty incredible - it takes a moment in real life and films it at a very high frame rate. When that moment is played back at a normal frame rate (24-30 frames per second) you get to see the action drawn out over a much longer period of time.
Like 19 hours...
The Slow Mo Guys were filming Pyrex kitchenware being subjected to heat and then rapidly cooled for some gorgeous fracturing action and decided to see how far they could push their Phantom camera system. That resulted in a pretty low resolution of 256x144 but a rate of 343,000 frames per second.
The final video lasted over 19 hours, which was just 5 seconds in real time. You can watch it below, and skip to the 10 hours 19 minute mark if you want to see the action starting.
It's hard to wrap your head around how long this takes to unfold, and also just how quick (relatively speaking) the cracking is when it finally occurs. That's a tiny fraction of a second impossible to see with the naked eye.
Also consider that this footage was actually shot outside on an extremely bright day and the massively high frame rate limited the light so much that it looks like it was almost pitch black. Here's a look at how it was all put together, and you can see how this speed actually freezes action at the 7.34 mark.
One of these fellows, Gavin Free, was the slow motion consultant on the Dredd movie, and you can really see why!