Cat C suddenly aggressive to Cat P

For the sake of ease, I’m using initials for my cats. My fiancé and I have four cats, and for the most part, they’ve all lived peacefully together. C and P have been close for years, with only the occasional playtime spat that they would resolve on their own after a couple of hours. P has some anxiety and has had issues with the other two cats, so she has her own room. Recently, P got sick and needed to be separated from C for about two weeks. During that time, C spent more time with G and R; R can be a bit aggressive, while G is more playful. C gets along with both of them well enough to live together in the apartment without too many fights or spats. Now that P is feeling better, I’ve started letting C back into the room with her, but suddenly C is hissing and growling at P, as if she doesn’t recognize her at all, while P seems perfectly content and unbothered. Their body language shows that both cats have forward-facing ears, tense faces and bodies, lowered tails, and their eyes seem normally dilated. C gets upset if P is just resting on the bed by herself. C isn’t usually very vocal, so it’s quite unusual for her to be this upset about a cat she used to cuddle and groom. The only time I’ve heard her growl before was when a stranger came into the apartment. I’m really confused about what’s going on. I can answer questions, but I’d appreciate any ideas about what might be happening so I can work on this myself. I don’t think C is sick, but I know cats can be good at hiding it. The only other behavioral change I’ve noticed is that she’s refusing to use the litter box outside of this room, which might just be a preference since it’s a litter bot and not a traditional pan. If this continues, I’ll definitely take her to the vet for a general check-up to be safe. But if this isn’t a medical issue, I’d like to try to handle it sooner rather than later.

It sounds like there may be a few things going on. Cats can be pretty sensitive to changes in their environment. Since C was separated from P for a while, she might be feeling territorial or stressed about P being back around.

@Emory
That makes sense. Sometimes, even a short separation can lead to a change in dynamics. Have you thought about reintroducing them slowly?

Tory said:
@Emory
That makes sense. Sometimes, even a short separation can lead to a change in dynamics. Have you thought about reintroducing them slowly?

I haven’t tried that yet. I was hoping it wouldn’t be necessary since they’ve known each other for so long. But maybe it would help.

I’ve had a similar situation with my cats. When one of them was sick and had to be separated, the others acted differently when reintroduced. It can be confusing for them.

Briar said:
I’ve had a similar situation with my cats. When one of them was sick and had to be separated, the others acted differently when reintroduced. It can be confusing for them.

Right? It’s all about their comfort levels. Giving them a chance to adjust to each other again might help ease the tension.

Also, sometimes illness can change how a cat perceives others. C might be feeling insecure or even a bit anxious herself after being around G and R more.

Neve said:
Also, sometimes illness can change how a cat perceives others. C might be feeling insecure or even a bit anxious herself after being around G and R more.

That’s a good point. I didn’t think about how her interactions with the other cats might affect her behavior towards P.

Neve said:
Also, sometimes illness can change how a cat perceives others. C might be feeling insecure or even a bit anxious herself after being around G and R more.

Yeah, and if P has been in her own room, C might see her as a stranger now. It’s all about reestablishing those bonds.

Don’t forget about the litter box issue. It can also be a sign of stress or a preference for the other setup. Have you tried different types of litter to see if that makes a difference?

Whit said:
Don’t forget about the litter box issue. It can also be a sign of stress or a preference for the other setup. Have you tried different types of litter to see if that makes a difference?

I haven’t yet. That might be worth exploring. It could help ease some of her discomfort if she prefers something different.

It’s great that you’re aware of the behavior changes. If you do see any further aggression, I’d suggest consulting with a vet to rule out any underlying health issues. It’s always better to be safe.

Reese said:
It’s great that you’re aware of the behavior changes. If you do see any further aggression, I’d suggest consulting with a vet to rule out any underlying health issues. It’s always better to be safe.

Absolutely, I’m planning to keep a close eye on them. If C’s behavior doesn’t improve, I’ll definitely take her in for a check-up.