This shows the trails of some sparks. Several objects spit them out as they move. Each of these objects belongs to one of four classes according to the colour of the sparks it spits:
- class 1 – objects that spit blue sparks,
- class 2 – objects that spit green sparks,
- class 3 – objects that spit flame-coloured sparks or
- class 4 – objects that spit whitish sparks.
Each class, in turn, belongs to one of two pairs:
- pair 1 – classes 1 and 4 or
- pair 2 – classes 2 and 3.
Each object accelerates with a constant magnitude of acceleration towards the closest object among those belonging to the other class in the pair to which its own class belongs.
Meanwhile, each object spits out sparks of the appropriate colour in the direction opposite to its acceleration. All the sparks move at the same speed and fade as they move.