I never expected to see this with my own eyes! It's a bit chilly here, about 10F (-12C), and I'd left a 2-liter bottle of Clear brand black cherry sugar free soda outdoors (so it would be cold). I brought it inside and went to pour a glass when BAM! it turned to ice as it was being poured! Don't believe me? Here's the video, taken less than an hour ago.
The "weird stuff we had when we were kids" referred to by the kid in the video (that would be Emma) was sodium acetate, which is known for being easy to get into a supersaturated state. (I did a Popular Science column about it and it's in my Mad Science book, so we had a couple gallons at one point.)
But this isn't a supersaturated solution, it's a supercooled liquid, which is much harder to achieve and keep stable. The fact that this soda was able to stay in this state at such a low temperature (probably not actually 10F/-12C, but definitely a long way below freezing) indicates that it was very pure (in the sense of free from particulate contamination) and that the plastic bottle had a very smooth inner surface.
I've heard of water bottles getting into this state when left absolutely still in cold weather, but they generally freeze solid as soon as they are disturbed. This stuff stayed liquid as I carried it in and poured several glasses full of it! In fact you'll notice there's a little pile of ice in the bottom of the glass at the start of the video. I didn't know it would happen when I poured the first glass, so of course I wasn't recording it. When I got out my camera and poured a second glass, it didn't freeze even as it was being poured (which is pretty astonishing, I think). So for the third glass I put in those seed crystals, which worked, and proved that it really was very much supercooled in the bottle.
Then we proceeded with dinner. The instant-ice was very spongy, kind of like marshmallow except it melted as you ate it.
A few days later Nick and I re-flimed it under better conditions: