Thanks for the links, those are pretty cool! But unfortunately, they are not the demo I'm talking about. The demo I remember came out in '97 before nvidia was a thing yet. At that point they only had the Riva 128 cards out. This was a DOS demo, not Windows; also the demo I had was much more primitive, and instead of the blob reflecting light, it was clear and only sort of "refracted" light. The wood floorboards or whatever were pretty low res and there wasn't really anything else in the scene. The other important part is that this demo did other things too, but I can't remember what they were. There were different "scenes" that it would play (it was a rolling demo I think). It was really the first cool thing in hardware-accelerated 3D that I'd ever seen, just as the Diamond Monster 3D cards were starting to sell well. It's obviously pretty obscure, probably written by a college student or something, and maybe I'll never find a copy. BTW speaking of which, does anyone remember "Funky Quadratics"? I'd like to see that again as well.
OH YEAH, I just remembered another demo I've been hunting for: This one came out in late '97 or thereafter, and it was a a rolling demo showing a toy train running along a track that wound through a child's bedroom, with toys all over the place. The camera followed it from behind as It would go past all the various 3d rendered toys and soforth. It might have been for Christmas or something like that. This one was definitely from a post on 3dfxmania.com.