I believe specific gravity.

Things like "how do you properly make a B-52?" ( http://www.cocktailhunter.com/bartender-guide/specific-gravi... ) or a Pousse Café ( https://youtu.be/4OJd_phsa5w )

Yes, particle velocity! I believe this clip is after I implemented metaballs too, so the particles blend together to make it feel more fluid-like.