www.google-analytics.com prevented me from seeing it, but I think I've seen it before. Supposedly, cats can do the same thing (albeit with their paws, not a brush).
The only thing my dogs ever learned to do was, after a case of, uh, "poopy-butt", was to sit on my living room carpet, lift their hind feet up in the air, and then scoot forward with their front legs, simultaneously cleaning and "scratching".
I tried it, it works.
(j/k, dammit)