Have you ever taken one of your cats to the vet and then return home and your other cat acts like it's never seen the cat before - greeting it with hisses, growls and swats?
This is called "non-recognition feline aggression" - yes, it's a real thing! "Non-recognition aggression can be dangerous for the cats and even be redirected to humans." says Dr. Borns-Weil, DVM, head of the Animal Behavior Clinic at Tufts University.
Here is what's happening:
Cats communicate most strongly with their noses - scent.
Each cat has a signature scent that is deposited on each other an the home environment, creating a communal scent of their home territory.
When the cat returns from the vet, his scent is overlaid with smells from the clinic.
The returning cat may have also released fear pheromones, or smell sick.
Upon return, the home cat recognizes these scents as a threat, or a reminder of something fearful they experienced.
The home cat cannot respond to the direct threat so he redirects the aggression to the returning cat.
How to mitigate it:
Desensitize cats to their carriers and car rides
Use pheromone, feline calming pheromones (plug ins and sprays)
Delay the reunion - do a mini version of cat introduction (found on our home page)
Make a gradual reintroduction
Scent swap: before going to the vet, rub each cat's cheek with a sock; seal the sock (separately) in a plastic bag and when the returning cat comes home rub him with both pairs of socks. Do not rub socks on the home cat.
It's interesting to note non-recognition aggression does not typically happen between cats and dog companions.