This is an example of Quartz Composer. In this I'm using a particle system, with a gaussian gradient input, as well as a gaussian gradient background. I'm using blend modes, and the kineme GL Logic Op. What the attempt was, was to make the outline of the circle in the middle deform, as the particles cross over the top of the circle. This is similar to the optical illusion of what you see when looking into water. This is obviously (hopefully) NOT an attempt at realism though!