The Liquib Whisk Tool is quite simple to use.  Just click the mouse on the source image to capture a small picture from that area.  Then, while the mouse button is still pressed, move the mouse according to your whims to drag that picture fragment around the screen, leaving a trail of edge colors following its path.  The size and shape of the captured picture can be configured, or set the Random option to be surprised!
Liquib Whisks