Indoor/outdoor aggression

[canopener]

When the weather is nice, I often let the cats have some outdoor time, either supervised in the back garden or out walking on a leash. Ciaran very much enjoys this while Kismet, who has a somewhat nervous temperament, often declines to partake. Which is fine. But the problem is when Ciaran comes back into the house. She will often hiss and posture at him almost as though she doesn’t recognize him. She also sometimes seems distressed when Ciaran and I are out back, meowing at the door but not wanting to come out.
I’m taking a desensitization approach to the latter but I’m not sure what to make of her reaction to Ciaran. Generally, they get along well, though Ciaran can get overbearing at times. For what it’s worth, Ciaran just seems to be mildly confused by her hostility and goes about his day. But I don’t like seeing Kismet get distressed and I don’t want it to have ramifications on their relationship long term.

 

[ArtNJ]

That is a known thing called non-recognition aggression. Turns out that cats recognize their buddies in large part by smell, so if a cat comes back from somewhere smelling different, it can be an issue. It more commonly comes up coming back from the vet or the groomer, and many indoor cats coexist quite well with indoor/outdoor cats. Nonetheless, that has to be what it is going on.

You might be able to solve the issue by keeping a towel/blanket well scented with Cairan's smell. Before he comes in, give him a rub down to rescent him with his own smell and get any outside smells off.

You should probably avoid the groomer and be especially careful with vet visits, since you might see a stronger reaction in those contexts. You might, for example, want to take them both to the vet together in a 2 cat carrier, even if only Ciaran has to go. Or maybe you just have a towel standing by for rescenting before coming back in the house.

(There could also be an element of redirected aggression in your cats situation. Thats when something stresses a cat, and the stressed cat lashes out at another cat or person that didn't cause the issue, but is nearby. I've never heard of that happening merely from the other cat going outside, usually it takes something more significant like a loud noise or spotting an enemy cat, but you mentioned your cat has a nervous temperment so it could perhaps play into it.)