The noise texture is being added to the object coordinates to displace the voronoi texture. The sum is added to another value that animates the displacement. The subtract node is probably unnecessary for a procedural texture, but Bartek put it in his video so it’s there for good measure (it offsets the offset so your texture is still projected from the origin). The animate value could routed through a combineRGB node to control the flow direction, but I haven’t done that yet. I am sure I am doing a terrible job of explaining this so here is the video where Bartek does a much better job (with visuals and everything). He gives more or less the same demo in the wood shader chapter of the shader forge series here on CGCookie.
