Cornstarch and water, mixed in the correct proportions, makes a "goo" that is very fun to work with. It works like a liquid if you let it flow, but if you push on it or put in under a lot of stress, it works like solid.
It turns out that quicksand works something like this. So, if you are ever in the situation of needing to walk across some quicksand (not likely, of course, but you never know!) do what Meara does in this clip: step quickly! As long as you move fast, the goo looks like a solid. If you slow down, as Meara does at the end of the clip.... Well, let's hope you have some friends around to pull you out!
This movie is in QuickTime format; if you need a plug-in to view it, you can get it here.
And if you want to make your own cornstarch and water goo (which, of course, you do - trust us!) you can find out how to do it on the Everyday Science page. Look at the links at the end of the "Mixtures" section.