Cannons and Quarters by Bryce Hixson
A small piece of dry ice is placed in a test tube, which is stoppered. As the dry ice sublimates, the pressure inside the test tube becomes too great for the stopper to contain, and the stopper flies off the tube.
Another piece of dry ice is placed on a quarter. When pressure is applied to the dry ice, it causes George Washington's teeth to chatter, producing a delightful high-pitched squeal, much to the delight of the kids.