Messing around with dry ice.
Wow, dry ice is cheap entertainment. A dollar a pound and we had a great time watching it and playing with it.
First we got bowls of water and threw a few chunks in to watch it boil.
Then we put some chips in a smaller bowl and squirted drops of water on it to see what would happen.
We also blew on it to see what kind of swirls it would make, then breathed it in to make ourselves cough.