Jelly

pull one side. the other side answers late.

a translucent jelly on a wooden table -- pull it anywhere, let go, and watch the wobble travel through it. fling it and it lands with a squash

A soft body has no single position. Push it at one point and the push does not move the object, it travels through it: the far side is still where it was for several tenths of a second, and then it overshoots. That delay is the whole difference between a solid and a jelly, and it is why a poke on a mattress, a calf muscle or a bus seat arrives somewhere else, late.

Concepts: elasticity, waves, soft-body.

An interactive you play with one thumb, on Wundr.