Cornflour is made from finely ground
corn; thats what it looks like to me.. It's used in
cooking as a thickening agent, and also in
HP Sauce.
What I used to do with it though is to make a
saturated solution of it with cold
water. This has the interesting properties of flowing like a
liquid, but fracturing like a solid when pushed around too fast and is an example of an
iostropic liquid (in contrast to a
thixotropic liquid like
tomato ketchup.