Have you ever seen water freeze instantly? This "Quick Clip" shows some of my personal experiences with making instant ice using a bottle of water supercooled in a freezer.
To get this "instant ice" effect, I put unopened bottles of water in the freezer for anywhere between 90 to 115 minutes. The water gets supercooled (below freezing), but does not actually freeze because the water doesn't contain enough impurities.
When it touches an ice crystal, it turns instantly to ice. It will also do this if the bottle is hit hard enough.
The clip at the end of the video above is a bottle that was frozen for nearly 2½ hours and the entire bottle froze immediately when I tried to unscrew the cap. Most of them won't make it that long.