Mean Cat just got meaner! Help?!

My cat Noelle is an 8 year old Main Coon mix girl.
Ever since we brought her home from the humaine society she's been a bit on the touchy side, and now with a dog and another cat, she's been pretty aggressive.

This being said, it usually happened that Gracie (the other kitty) could approach and sniff Noelle. And on occasion, Noelle would even "lower herself" (she's very prideful) to clean Gracie's head.
But now, Noelle hisses evilly whenever Gracie gets in sight.
If Gracie advances, Noelle hisses again and tears away down the hall. She's never acted this way before, and it's weird... plus it's scaring Gracie, who just wants to play.
We thought that maybe Noelle was concerned that her dominant place in the furry side of the family was being threatened, but this would be sort of paranoia on Noelle's part, because both Gracie and Tuna (my dog) are verysubmissive, and would never think of taking Noelle's place away from her.

Noelle does not appear to be sick. She's eating, cleaning, moving, pooping (goodness knows, she's pooping ) just like normal. This is the only "symptom."
So is she not physically sick but kind of sick in the head? I have no idea what could have caused it, if that was the case...
Help, please??!!

She could be sick.
Cats are small, prey animals and very, very good at hiding illnesses and are often quite seriously sick before they show any signs that we would recognise as symptoms.
It could be that Gracie is sick and Noelle can smell a change in her.

I would take both cats to the vet and completely rule out illness before tackling this as behavioral.
You say Noelle is 8 yes old, if she hasn't had it done yet, she needs a complete senior panel done.

Once health issues are ruled out by a vet, the best advice I have is to do re-introductions following the steps posted here

You're saying that they could be sick, though they aren't showing it, still have appetites, and aren't coughing, sneezing, etc.? If so, then they ARE really good at hiding it!

I'm wondering if there has been a change in her eyesight. Maybe she is not seeing well for whatever reason and she's just being defensive of the other kitty.

Originally Posted by Audrey_

You're saying that they could be sick, though they aren't showing it, still have appetites, and aren't coughing, sneezing, etc.? If so, then they ARE really good at hiding it!

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Yes, one of them very well could be sick, even something minor such as a slight change in metabolism would alter their scent enough for one not to fully recognize the other.
Usually, the one getting attacked is the one that something has changed with.


Not to scare you into thinking it is something serious, but just as an example, a cat that I had had for many years was suddenly being avoided and sometimes even attacked by his best friend fully a month before he showed any outward signs of being sick.
He was later diagnosed with lymphoma.
Cats are super sensitive to even the slightest change in scent.

What arlyn is saying is correct. The nature of the cat is to hide sickness. So the way you most often find that something is wrong is a change in behavior.

Yep, I would venture to say that Gracie is sick and needs a vet. She may not smell the same as before and cats are very responsive to smells we can't even get close to. They are adept at hiding illness because they are low on the food chain. They know that showing any type of weakness could mean they end up as lunch. There are therapy cats that I know of who let nurses and aides know when a resident is going to be sick- even die. They camp outside the room and if let in, they will jump on the bed and snuggle with the elderly patient until he-she passes. Cats are extraordinary beings- yours might be trying to tell you something- the question always is- is the owner listening?

I have a similar problem and none of my cats are sick, I have two dsh and a ragdoll, it happens between my two dsh, my bossy cat sometimes just hisses and growls at the other cat whenever the mood takes her, this has been going on for sometime now ever since I adopted the ragdoll, with my cats it just seems like redirected agression.

Originally Posted by Tallulah

I have a similar problem and none of my cats are sick, I have two dsh and a ragdoll, it happens between my two dsh, my bossy cat sometimes just hisses and growls at the other cat whenever the mood takes her, this has been going on for sometime now ever since I adopted the ragdoll, with my cats it just seems like redirected agression.

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You are talking about routine, you say "sometimes". The OP says its a new behavior completely.