Taken out of context, this first video is pure magic. It appears that balloons will self-inflate once taken out of liquid nitrogen. Just watch this and form a hypothesis about what's going on:

All right, Dr. Science, let's dig in and see what's actually going on:

So in the first video, we saw a bunch of pre-inflated balloons that had been cooled down to the point that the air inside turned to a liquid state. They were then inserted into canisters of liquid nitrogen (or perhaps they'd been cooled in the same canister, hard to say), and simply dumped out again. Neat, right?

The one bummer: This ruins my "instant balloon party surprise" idea. Really seems like a lot of work when you get right down to it. Plus there were several popped balloons! Oh well, science, am I right!?