If he has some liquid hydrogen on hand, you should go pour yourself a nice big glass, sit back and watch what happens when the stuff is left unattended.
It evaporates pretty fast from a dewar. Most of what we get is compressed, and sometimes that’s absorbed into a metal sponge of some sort.
The liquid is much colder than nitrogen, about 20K, and it’s much less dense, a liter of LH2 weighs only 70 grams, where water weighs 1000 grams.
It’s pretty flammable, naturally.