Regarding Helen's cornstarch trick - If you take that concoction in your hand, and squeeze it, it feels solid, but then let your hand relax, and it runs out of your hand. Quite something! I used to do demonstrations for elementary school classes about chemistry, and that was always a fun one. They call it "Magic Mud" up here. There's a kids' magazine about science called OWL Magazine, and in it, Dr. Zed (not Zee!) has an experiment every month. One of his most famous is the Magic Mud.