We keep a bowl of water outside for the cats to drink. I recently bought a bowl that said it was resistant to algae and other growth. Since it's been raining a lot recently it was full to the top.
Last night we actually got pretty cold, below freezing. This morning when I took the dog out I noticed the cat's water bowl looked like it had something stuck in it. Upon closer inspection I found that it had an ice spike growing out of it. I thought maybe a leaf or stick blew into the bowl but no it was clear ice.
I'm guessing a combination of the bowl's plastic properties, the fact that it wouldn't break (like many of the past bowls we used) and how the temperature did it's thing last night created this oddity.
I don't doubt there are chemists who could easily explain this, but it's still pretty cool.
Below are pictures: