A darkfield tank of drifting zooplankton — elongated copepods trailing antennae and forked tails, round ciliates fringed with beating cilia, and oval daphnia with a bright compound eye — each swimming its own path while a wandering light draws the whole swarm into positive phototaxis, punctuated by startle jerks. The pointer becomes the light they chase, a press scatters them in fright, and scroll thins or crowds the swarm.