This is a magical substance called oobleck. It's just a mixture of corn starch and water. What could possibly be freaking me out about a little corn starch and water? Well its MAGICAL!
When you mix it in a huge pool type thing, you can literally walk across it. Only if you move quickly though, if you stand still it will swallow you up! Its freaky and I have never wanted to try anything more in my entire life! Watch this video of...well...I have no idea why these guys are doing it but its cool looking!
Why this works has a relatively simple explanation: stepping on the oobleck creates impact on it, but the water is driven away faster than the starch. This means that as long as you only step on it briefly, the area supporting your foot will consist solely of the solid particles, which jam into place in a particularly sturdy matrix.
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