TEN
This shows the trails of some specks of colour as they emerge from ten moving bodies. The bodies come in two contrasting breeds; five belong to one breed and five belong to the other. Each body accelerates towards the closest body of the opposite breed with a constant magnitude of acceleration.
At regular intervals, each body emits a burst of ten specks of colour in a narrow fan to either side of the direction opposite to its velocity. Each speck of colour emerges at a speed of ten times the speed of the body that emits it. After that, its velocity doesn’t change. Ten such intervals after the speck of colour emerges, it disappears.
Over the course of its life, each speck changes colour. Towards the end, or if it passes close to a body of the opposite breed to the one that emitted it, the speck of colour grows and loses opacity.