My method studios-inspired expiriment with mocap animations from mixamo.
I used this also to get some practise with procedural constraint networks and the SOP solver in Houdini.
Each of the 8000 spheres is spring-constrained to a skeleton-animated point, then after a while the constraints can "break", switching to the other animation target and starting with zero strength, which allows the particles to almost escape for a short while before the constraint strength increases and the target animation is reached again.
Particle shader has velocity based emission.
Rendered amazingly fast (around 90 min. for 720p 300 frames on 980 gtx) by Redshift Renderer.