How much hissing should I tolerate from old cat getting used to new cat?

Question

Just going to start with the basic info:

Cat 1: Pancake (female, spayed)

• 2 years old
• lived with us for 1.5 years
• came from shelter, abandoned at birth
• very anxious, scared of everything

Cat 2: Bean (male, neutered)

• 1.5 years old
• also came from shelter, lived with siblings & mother there until adoption
• lived with us for about 3 weeks
• very passive and outgoing, just wants to play, shows no aggressive behaviour

Backstory

We brought home Bean, our new cat, in a cat carrier and gave Pancake, our existing cat, a chance to smell him and say hi. The initial meeting did not go well because it took a long time for Pancake to realize there was another cat in the carrier, got close to the carrier, and freaked out when she realized what was going on.

For the next 5 days we kept Bean in the office with his own essentials, and Pancake got the rest of the house. I started by putting their food bowls next to the door so they could come together to eat and smell each other under the door, but Pancake refused to eat unless I moved it far away. We slowly started swapping their spaces to let Pancake become accustomed to his smell.

Since then we've started bringing them together with treats and toys involved. Bean is content playing with toys and having treats, but Pancake just keeps staring Bean down and hissing. So far that's the only aggressive behaviour we've seen from Pancake - there has been no back arching, no tail-poofing and no ears-back snarling.

Bean is extremely passive and just watches her, which I think makes Pancake even more anxious. He definitely wants to play but keeps his distance based on her behaviour, he seems very well-mannered and socialized.

Today, we've reached just over 3 weeks since bringing home Bean. Pancake is acting super strange and I'm not sure how to proceed.

Problem

Pancake wants to follow Bean around, get close to him, then snarl and hiss and run away. When they're together, Bean seems pretty much unbothered by her presence, but Pancake can't focus on anything else (treats, toys, pets), and when we try to pet her, she hisses and snarls at us. Keep in mind that Pancake has some pretty severe kitty anxiety and will sometimes hiss/snarl at me if I walk into a room and take her by surprise. We've used cat calming spray to surprisingly great effect in the past and have been using it liberally here!

If we put Bean back in the office away from Pancake, she immediately starts scratching at the door and wants in. So I let her in, and she starts hissing and snarling, then runs away. Rinse and repeat.

I'm not sure how to proceed because her behaviour is so confusing to me. She seems keen on being near him/keeping tabs on him, but gets very angry when they come together. Duality of cat?

My question is: should I keep them separated for the timing being, or let them hang out more despite the hissing? How much hissing should I tolerate before I separate them? I don't want to establish a dynamic of violence between them, but I also don't want to keep them separated forever.

Answer 1

Most people consider hissing a sign of aggression, but honestly it's "just" a form of communication. Hissing alone is no aggressive act, it's more like a warning "come no closer!". So in the end, although it would be preferable if Pancake didn't hiss, it would be much worse if she attacked Bean instead of hissing.

The constant following around sounds to me like Pancake still considers Bean an intruder in her territory. She has not accepted him as a housemate. Given more time, she may or may not ever accept him. I also have 2 cats that don't want anything to do with each other, but they have more than enough space to avoid each other. And the more insecure and sensitive one of my cats is also the one who doesn't accept the other. I don't know if that is coincidence or a trait of insecure cats in general, but you have to be prepared for the fact that Pancake may never accept Bean.

And honestly, 3 weeks for introducing new cats is not that much time. Cats are territorial and many resist change. Unfortunately, trying to force them to interact with each other (like swapping rooms or putting food bowl close together) can increase the stress and decrease the acceptance.

Personally, I would try to calm Pancake down some. Give her a dedicated room that is hers alone (Bean is not allowed there, the room and all objects in there should only smell like Pancake) with all her food and water bowls, litter box and cat tree. Give her time in that room to calm down every day. She should probably sleep there and spend some hours there each day.

When you let both cats interact, let them do it in their own way and time. Don't interfere too much like trying to pet Pancake while she interacts with Bean. That can be overwhelming and disturb the process of familiarization. You can pet Bean to keep him calm, but completely ignore Pancake as long as she doesn't attack. Don't even look at Pancake (looking a cat in the eyes is a warning sign, just like hissing).

And consider helping Pancake feel safe by giving her more vertical space to approach Bean or run from him. "Cat shelves" or similar furniture, as described in this question, can help.

Answer 2

Hissing isn't necessarily an aggressive behavior. It's more the way a cat communicates, "stay away," which could be motivated by fear or aggression. I'm also guessing in this case is more fear motivated than aggression. However, even if it is a fear response, ideally you want both cats to be happy, rather than having one being afraid all the time.

Keep up your efforts to distract them from each other.

Your general approach seems spot-on. I think the one area that needs work is the exercise of putting them in the same room and trying to distract them with food or play. You need to really distract Pancake in order to get this to work properly. There's a few things you can still try to see if you can get this to work:

1. Figure out a particularly high value treat for Pancake. You might try treats that are unpleasantly smelly to humans, such as fish flakes, as cats seem to really like strong food smells, or churu which many cats seem to like a lot.

2. If the cat is less food motivated, you could try play, but you need to be really insistent and energetic to really keep the cat's attention.

3. It may even help to get a big piece of cardboard and physically block Pancake's view of Bean whenever her attention starts to wander.

Provide Pancake with ways to get away from Bean.

Pancake may also calm down about Bean's existence if she is more able to keep an eye on him from a safe place. Cat furniture is ideal for this, because they can go up there, and they will feel much safer with elevation separating them.

If you can, arrange lots of cat furniture and possibly also your regular furniture, so that your cats can have alternative paths throughout the home.

Ask your vet about anxiety.

It may help to discuss Pancake's situation with your vet. Pancake sounds possibly generally anxious, and the vet may have more advice to help lessen the anxiety.

Answer 3

It sounds like to me that Pancake is acting out of fear and doesn't really know how to properly socialize with other cats, which would explain why she freaks out whereas Bean doesn't (despite her hissing). And that fear would also explain why she attacks you if you try to pet her with Bean around, she takes that fear and stress out on you. However cats are naturally curious creatures, so when she feels a little safer (like when Bean is looking the other way), she might feel confident enough to approach and sniff at him but any slight movements or sounds could cause her to freak out. To be clear, I don't know if this is exactly what's happening but this is what I'm imagining is going on since I've dealt with cats like this or scenarios where cats acted like this. Personally, given Pancake's history, this is perfectly understandable.

I suggest to let her explore Bean and approach him, she's a cat and cats are always going to want to satisfy that curiosity. However, you should be right there to step in if things go wrong. And I'm mainly thinking of Bean here. Pancake sounds like she's acting out of fear and so is more likely to run or overreact if Bean makes one wrong move. So if Pancake is up to it, I'd be holding/petting Bean to try and keep him still while Pancake checks him out but also be ready to grab Pancake in case she gets freaked out and takes that fear out on Bean. Of course, I'd only do this if you know your cats well and aren't afraid to get scratched cause when cats are in this fear state, your presence might only stress them out more and take it out on you. So you should approach slowly and WITH Pancake (that way if your presence freaks her out, she's nowhere near you or Bean at that point and so is more likely to run than attack) and make slow movements the entire time. Getting to know Bean in this way will hopefully be enough to let her know he isn't an object to be afraid of.

Ultimately hissing isn't a big problem, cats usually do this as a sign of fear. As long as Pancake is given room to escape, I wouldn't be too concerned by it. If things don't get better between the two despite plenty of time for Pancake to get close to the newcomer, then I'd suggest giving Pancake a quiet place she can go to retreat/hide from Bean that Bean is ideally not allowed. But I do think that if you just allow Pancake to get close to Bean like she wants and give her time, that she will at least tolerate him and be able to relax in his presence. One last thing I'd like to add is that since Pancake is so afraid of Bean, it's vital you make sure Bean doesn't do any small thing to scare Pancake (it won't be hard). So maybe until Pancake calms down at least a little around Bean, you only keep them together when you can watch them. Even something as small as Bean trying to play with Pancake could cause her to freak out and see it as Bean being aggressive towards her.