The percentage of balls held fixed can be changed by the slider, and the "Restart" button can be used to scatter the balls and restart their movements. You can try out different values and see which one you like the best.
The original idea was this: each ball travels on a sine-wave path (kind of like a spring) between a randomly-chosen pair of two other balls.
It was soon discovered that if all balls are free to move like this, they all quickly collapse to a single point. Thus, some number of balls are held fixed (5% by default). The result is a slightly organic-seeming emergent motion.