1. Dilatants - fluids that get more solid when stressed. The classic example is a mixture of cornflour and water - it's runny until you hit it when it becomes solid.Link (via Neatorama)
This video shows how that it possible to run across an apparently liquid pool of the stuff because your footfalls solidify it. If you stop, you sink.
I like this video better though - it shows how sound waves from a subwoofer produce interesting shapes in a dilatant. If you want to have a go yourself, try this recipe.