system
Given the following post, respond as if you're commenting on Reddit:
human
Ice spontaneously appeared in my water?

I grabbed a 6 oz styrofoam cup from an inverted stack, so I know nothing was in the cup. I went to the water cooler. It's got a cold and regular spout. I put cold water into my cup. Looking at the water flow into the cup so I would know when to stop.  I put said cup to my lips and took a sip. It was really cold so I looked into the cup and there was what looked like crumpled up saran wrap so I freaked for a second. It was literally 80% ice in the cup in a huge flowing looking blob. How the f--- did that happen? I went back to the water cooler but could not make it happen again.
gpt
You just discovered the concept of super cooling a liquid.  You can take a liquid below the temperature they would normally freeze at if there are no rough surfaces inside the vessel they're held in.  If there's no nucleation sites inside the water cooler, when it comes out the water will solidify on contact to a bumpy surface.

It's also the same reason you need to microwave a liquid with a plastic spoon or whatnot in the liquid.  If there are no nucleation sites in a vessel when you heat it, the liquid can suddenly burst into a full boil when you go to retrieve it.