This scene shows caustic effects on the ground of a swimming pool when the sun light is refracted through the water waves. The water surface is done by a simple f(x,y)-function of 3 summed sinoids. If the phase of these sine-functions is increased, the water comes to motion, which reflects effectful in the caustics on the walls and the ground:
Water Animation (320x240 mpeg1, 24 frames, 173k)

Excuse me for the bad quality of this movie clip (noise and color flicker) I gave it only 7 million primary light rays per frame, but even that took my 233MHz-PII two days to render the complete animation.