This is a modified version of the sparks of the previous demo. Now, instead of slowly bouncing around, the sparkers frantically chase a little glowing dot around.
They don't chase very intelligently, though; they accellerate as quickly as they can in the direction of the dot. Hence, they tend to overshoot the dot and have to circle back around, or bounce off the walls. Their poor pursuit strategy makes for interesting visual effects, though.
I saw this "swarm attacking a dot" idea in an X-Windows screen saver.
Link to the source code.