Via Twitter:
Q: Hey Jen, one of my kitties has some health issues and when he comes home from vet my other cats are mean to him for a bit. Any advice?
A: As crazy as it sounds, your other cats smell the vet scents on your kitty and don't recognize him. Make sure to get his home scents put back on before reintroducing him into the fold. This can be done by taking a sock or other cloth and rubbing it on your kitty prior the vet, then rub that sock on the cat that is most offended by his return. Be sure to get a good rub on their cheeks. Put the sock in a bag. When you get back from the vet, place vet kitty in a separate room. Give him some time to groom himself, the take the sock and rub it all over him. This places the familiar scents back on him. Reintroduce him to the other cats via a cracked open door. If the cats don't seem upset, let him out to be with them. If they still seem upset, give him more time in the room, then have a positive activity like treats or playtime with all of the cats together.