eta: we went to the vet anyway, just in case. vet said it hadn't slipped far enough to worry but if it slipped more to come back. and then zilli crapped all over the cat carrier on the way home. oh, god, the stench. :/
eta, again: I think the vet is wrong. I don't know if the cast slipped further or what, but Zilli's not using his leg at all properly now and is trying to shake the cast off with a lot more vehemence than previously, and the proper vet (this one is the weekend guy) said if he stopped using his leg to bring him in. It is not easy to write when you're listening intently for any small sound that might be the cat in pain or danger. -sigh-