You know, for all the R/S fics I've read, I don't think I've ever actually read the Moony porn in the pairing! This was way hot, oh man, but then, it certainly doesn't hurt that I have a thing for Sirius being overwhelmed! :3
This... Sirius shouted in surprise, arms coming up to protect himself, forearms pressing into the fur-covered chest. ...was an exceptionally vivid image!