OK, this is not an secret: this block is based on the work done by nbremer on the gooey effect (cf. the original block, and More fun data visualizations with the gooey effect).
In this block, the resulting image is produced by applying a filter on moving circles. The filter is the same as the one used to produce the gooey effect, except that it uses an extra step which detects edges (feConvolveMatrix).