I can remember making small batches of cornstarch+water (a.k.a 'ooblick' or 'oobleck') when I was younger. For those who don't know, it behaves in an unusual way: pouring and splattering like a liquid, but turning solid temporarily when pressure is applied.
Seeing someone playing in a whole pool of it (and hearing the splattering, squelching and sucking sounds) is quite remarkable, and even better when it's Stella, with her obvious genuine enthusiasm for getting messy. (Also this might be just a personal kink, but I like the one-piece swimsuit worn in this and a few other of Stella's videos; I like the appearance of them generally, and there's something about swimwear being worn for not quite its intended purpose: getting wet, but with something other than water.)
If I had to choose just one video from the whole of umd.net, it would probably be this one, for both its quality and uniqueness.
mattmess 12/9/19