Pull it.
Rip it.
Put it back.
A lattice inside. The jelly is a grid of small cells joined by bonds. They keep their spacing and their volume, like a real gel does, and a smooth skin follows them.
Bonds snap. Pull a bond past the tear strength for a few milliseconds and it breaks, then its neighbours take the load, so the tear runs ragged through the jelly.
The knife cuts a plane through your stroke and the view direction: every bond that crosses it breaks, and both sides get a flat glassy face.
Pieces are found by walking the bonds. Each connected group becomes its own wobbling soft body, up to 48.
Smooshing re-bonds two pieces where they touch, and the skin merges. All sound is synthesised live from noise and oscillators.