I thought about that, but the pet stores around here were closed by the time that popped into my head. I did try that years ago when Chessie and Casey, but it had no effect that I could see at the time, which is why I've never used it since.

Things seem to be calming down. Around 11:45PM (11 1/2 hours after getting back from the vet's office), Casey was in the cat tree in the living room. Smokey got up on the cabinet next to the cat tree, and they touched noses without any hissing or growling. About 15 minutes later, Smokey started in again. It's like at the vet's office, Casey was the aggressive one, and when they came home, the switched roles. Casey hisses and growls, but only after Smokey starts in. After several minutes of their growling back and forth in the kitchen, they laid down at opposite ends of the living room while I watched a movie. They've been calm since.

I did try the dryer sheet idea, but both of them growled and hissed at me when I tried to rub them with it. They've been grooming themselves quite a bit, and they've been really wanting to rub on me this evening, which is helping to get my scent on them and spread their scent to each other through me.