1. Step one: fill a bottle with liquid nitrogen
2. Step two: close the bottle, throw it in the garbage can, fill it with ping pong balls
3. Step three: cover your ears
4. Step four: clean up
5. Here’s the original video
It’s not entirely clear what this demo is trying to teach, beyond this: the reason the bottle explodes is because liquid nitrogen becomes a gas at room temperature. Nitrogen takes up more space as a gas than as a liquid, causing the closed bottle to rupture violently. The ping pong balls, I think, are mostly just for show.