What you are about to see is called the ‘fluidized bed effect’ by some. It is created by blowing massive amounts of air evenly through huge masses of sand, rendering the sand into an almost liquid-like physical state, as seen here.
But below you’ll see NASA engineer Mark Rober filling a hot tub with sand and then aerating it to create the same effect, making the sand look like and act like a hot tub filled with actual water.
Not only is it cool but it looks like a helluva lot of fun to play in, too:
It is like quicksand that won’t kill you. Doesn’t get much cooler than that. Now it’s time for me to die trying to go recreate this in my backyard.
Wish me luck!