We keep liquid nitrogen around mainly to make ice cream with. One idle day we decided to play with it a bit. First, we thought we'd see how much harder it was to freeze alcohol than water. A friend had sold me some Everclear (95% ethanol) a few years before. I'd never touched it, and this seemed like a good occasion to crack it. What followed was the single most serendipitous liquid-nitrogen discovery we've made: if properly cooled, Everclear enters a highly viscous state in which it will pour off of a spoon like molten glass! It requires a bit of care, cooling it just the right amount while stirring constantly. If it's overcooled, it may remain in a vitrified state but it will harden so that it's uninteresting. In retrospect, it seems likely that the very rapid cooling that occurs with liquid nitrogen plays a role, since fast quenching prevents the development of large crystals in many materials. Vodka (40% ethanol) doesn't behave the same - no matter how rapidly and precisely we cooled it, it transitioned from liquid to solid with no viscous phase. The 75% ethanol psuedo-Everclear that's sold in California can be made to vitrify, but it's much more touchy; it really wants to solidify.

Other things we played with that day:
Froze an orange. When dropped, it shattered but not in a particularly entertaining way.
Dropped a disposable butane lighter into a big bowl of liquid nitrogen, figuring the butane in the lighter would freeze inside it; then we could crack it open and light the butane. Instead, as we all stood by in close proximity, the lighter shattered and the still gaseous butane exploded out, blasting liquid nitrogen all over the place. Watch Three Foolish Geeks Jump. I decided to try an aluminum cylinder of butane instead; we did that a few days later.

Later that year, Mike experimented with a liquid nitrogen powered rocket, with results chronicled in this icb log.

A few years later I made butane ice cubes for the Mad Science Fair.

More LN₂ fun is described in ubws' 1001 things to do with Liquid Nitrogen page.