So why is it that when I bring home my cats that have been groomed the other cats hiss, or they hiss at each other? Jealousy perhaps? No. Cats have very poor eyesight by nature, yet their sense of smell is 40 times that of a human being. They don’t recognize each other. Even if I don’t use any conditioning, finishing sprays, they smell different. The same holds true of a cat who has been to the vet clinic. Separate them for awhile, use Flower Essences or Phermones to calm them down. You might try some interactive play as well. It shouldn’t last long. Don’t panic. They will work it out.