When last we visited one-time NASA engineer and World’s Greatest Dad Mark Rober, he was dousing kids with the largest Super Soaker in recorded history. Now, he’s making the neighbors jealous by using an old trick that turns sand into liquid and filling a hot tub with the stuff.

To clarify: This is not quicksand. Rober is not dooming those he invites in the tub to a death known only to characters in 1950s safari movies. Rather, the process involves adding air to the sand in “just the right way”—it took him many, many tries to get right—which then allows each grain of sand to exist in a state of equilibrium that turns it into a “liquified soup.”

The best part? The moment you turn the air off, the sand immediately reverts to its natural form, thus trapping anything inside of it. So, if you’re doing this at home, avoid any and all dunking.

You can do it at home, too, as Rober explains both the science behind the phenomenon and the process of making it happen. Then you too can drop cinder blocks and giant, weighted trash cans into it like Rober and his cadre of moppets do.