I heard a sharp, not exactly pained, MEOW! and went downstairs to investigate. Zilli was sitting about three feet away from his cast, licking his paw.
I think the little shit outsmarted it. Judging from its location--right next to the bookcase, where I'd seen him lying with his leg under it earlier--I think he figured out that if it was slipping he could get it off, and I think he put his leg under the bookcase and scraped it off. As shadowhwk said, "...gotta admire the thinking that up, but BAD KITTY"
I have put the little monster into his cat carrier, because there's absolutely no other way to prevent him from getting around, and while he may be all right (although his poor little leg is rather shriveled-looking) I would rather not explore his okay-ness by having him doing normal cat things like stairs and jumping and climbing. Right now his primary interest (not that I can blame him) is washing his foot. I think I'll let him do that for a while, but I expect I'm going to have to put the horrible collar on him after a bit, because there are raw spots and I don't want him to damage himself.
I have this idea that ambar will be reading this and thinking, "Well, *you're* the one who wanted a Bobtail...!"