I have been playing with particle systems that have individual position and velocity but are also affected by other particles and the environment. In this case there are hidden “hotspots” in the field that affect the particles’ velocity vectors.
When a particle is within a certain distance of the circular hotspot its velocity is scaled to either slow it down or speed it up. Additionally it is partially pulled towards the center of the hotspot with a variable amount of ‘suction’. these effects combine to disturb the otherwise smooth and rhythmic marble field.