Help! Inexplicably grouchy cat!

OK, my fourteen-year-old shorthair, Smudge, has been back from her big adventure for two full months now. Her leg has healed, although she’s still short some fur. She’s put her missing weight back on. She’s even regained her desire to sit in a screen window & safely experience outside smells. (And complaining loudly when I won’t open the window, just because it’s, like, twenty degrees F outside.)

BUT … she is still not getting along with our other cat.

When she first came back, she was just generally nervous. And after her surgery, the younger cat kept trying to nuzzle at her stitches & getting swatted. They’ve always had some little tussles at times, especially when she’s being especially moronic and irritating. (Sandy has an estimated I.Q. of negative seventy, and annoys all of us at times.)

But now … everytime they’re in the same room and not both sleeping, it turns into a huge catfight. And even Sandy, who has never shown any signs of being able to store anything in long-term memory more complicated than the last known location of the food dish (if that), has started to learn to avoid her. They used to get along very well, most of the time at least, but now Smudge seems to be convinced that she’s an Enemy Cat, like the ones she hisses at through the window when they wander into our yard.

Anyone have any advice on helping these two kiss and make up, or whatever the feline equivalent is?

You might try Feliway spray or diffusers. They contain some kind of cat-calming hormone. They weren’t quite enough to bring harmony to our two cats, but they seemed to tame it a little bit. Since your cats got along previously, maybe this would do the trick.

That looks interesting! I’ll give it a try …

You could try moving. Or putting the two of them together in a small bathroom for two weeks to just sort it out by themselves. Worked for us. (Note: the bathroom jail was a result of the move and not trusting cats around half empty boxes - the social reprogramming was an unexpected benefit.)

Take her back to the vet and make sure she doesn’t have an infection that you haven’t noticed.

Has her thyroid level been checked? Problems with that can lead to irritability.

Aside from getting her to the vets to check for some other ailment that’s upsetting her, or trying Feliway, the only other thing I would have done is maybe try a little bit of Rescue Remedy. A couple of drops on her food is all you need and that can be great for de-stressing a cat.

I would second every piece of advice given so far. The trick is to do them in the most appropriate order.

EDIT: the rescue remedy advice was not there when I was typing and I would not suggest it.

Start with the vet trip, I gather?

No problem trying FeliWay (OTC), but any geriatric animal with behavioral changes should be examined to rule out biochemical causes. As a last resort, I have seen great success with anxietiolytic medications.