Will my cats ever be friends again after one went on ‘vacation’?

A cat owner asked the above question on a well-known website (metafilter.com). I’d like to try and answer the question. The person has two five-year-old indoor cats who are siblings. One of them escaped the home and spent two days under the house before he was recovered. His brother now hisses and growls at him and the owner wants to fix the problem urgently.

Cat nose and sense of smell

Two useful tags. Click either to see the articles:- Toxic to cats | Dangers to cats

Feline non-recognition aggression

The problem is described as “feline non-recognition aggression”. I’m sure lots of cat owners have experienced it. Inexplicably, a cat who was friendly towards another cat in the household becomes hostile. The likely event which could have caused this is because the ‘victim’ has lost his natural smell.

It is not the separation of the cats which caused one brother to become hostile to the other. It is the fact that the brother who remained in the house no longer recognises his sibling. He is suddenly confronted with a strange cat and becomes hostile towards him because domestic cats are generally territorial. Although domestic cats have become far more sociable over thousands of years of domestication.

Coat got dirty?

So, in this example, when the sibling was under the house for two days I’d suggest that he picked up some odors on his coat. Perhaps he rested on some dirty ground or items or perhaps there was something in the air which has become embedded in his coat.

Whatever happened, he no longer smells the same and therefore his brother can’t recognise him because domestic cats rely tremendously on their sense of smell to recognise both their owner and other cats. Sight also plays a part but if the nose does not recognise the ‘creature’ opposite him, the fact that he can recognise the cat or person by sight does not change the outcome. The nose takes priority.

Clean coat and let cat self-groom

In this instance, I would recommend that the owner gently wipes down the cat who escaped with a damp cloth. She or he should then keep the cats apart for a while if necessary during which the ‘victim’ cat will groom himself sufficiently to put his natural smell back on his fur. This shouldn’t take too long but it depends upon the cats.


The owner says that he has separated the cats for a few days. This should be more than enough time. Apparently it isn’t in this instance. Separating them may make the matter worse beyond a certain timeframe. I would reunite them because by now the “stranger” cat should have his natural scent back and be recognised. Keeping them physically separate may reinforce the mental separation.

4 thoughts on “Will my cats ever be friends again after one went on ‘vacation’?”

  1. Cats don’t lose the ability to recognise their cohabitee cats.

    They are often traumatised by the sudden absence of their close cohabitee. The smell aspect, is at best secondary, a reinforcer of the shock of absence/return.

    Think of the group of likely behaviours of the cat steward when a beloved cat goes missing.

    Humans reveal the results of all their stresses, even when they think they don’t or try not to. Also the stink of human fear/anxiety, the cat responds strongly to this and also the emotional trauma of their companion on return, be it from the vet or from being lost.

    Cats do not forget who the returning cat is, they are not idiots with no long term memory of shape, form or smell. Bum sniffing will confirm who the cat is as well.

    Humans come up with these explanations/judgements to bolster their erroneous belief that humans are superior to other species. Yep, humans are that insecure.

    Separating the cats is about the worst thing to do. Close supervision, calm and kindness, are the best way to deal with this. Scent mingling will help, but like most matters pertaining to humans interacting with other species the outcome will be predicted by the actions of the human.

    I have never had this occur with any cats I have cared for. That is a lot of cats over my whole life. Not one hiss of fear, not one fight on return of a missing cat or a protracted absence at the vet surgery. I believe this phenomenon comes about when there is something amiss in the home situation and the cat’s behaviour is not well observed, understood and humans allow their stresses, fears, relief to swamp the situation.

    One cannot emphasise the importance of calm when caring for other species.

    Ask Metafilter is heaving with Qs from clueless cat stewards. Often the language they use to describe companion cats behaviour indicates that all is not well between cats, home & steward.

    • Thanks Jane. The feline non-recognition aggression problem occurred with one my cats many years ago. They were siblings. The female fell into a tub of solid white paint! She traipsed over the carpet! I had to bathe her which removed her scent. Her brother hissed at her. She groomed herself and within a few hours all was well again.

      • What a horrible accident! I wonder if it isn’t a case of non-recognition, rather the hiss was one of alarm/fear, with the newly bathed sibling? I am glad all was well in the end. Sounds like you handled it very well.

        Jeff Masson is an interesting author to explore on interpretation of fear & aggression by humans in other non human species.

        …also Jonathan Balcombe.

        • I had a similar experience, but it only lasted a day. The aggression came from the cat that got outside rather than the one at home.

          I have siblings, a male and a female, Hansel and Gretel, both indoor-only. At the time they were both still very young, I don’t remember if they still were older kittens or a little over a year old. My girl got out as my elderly father was bringing in groceries. I wasn’t at home at the time, but my father told me that she first went along the narrow pedestrian path to another house, then turned back, run, and hid under the bush next to my door. My father didn’t know how to get her out, hadn’t thought of calling me, but was just checking on her. After about 3 hours she came back, saw her brother, run straight to him and attacked. They’d been play-fighting before, but this was different. He got scared – in spite of being 1.5 her size – run into a cat tunnel I’d just bought for him, and defecated there, probably from stress, then jumped on a kitchen counter and hid in the corner.

          When I got home from work I saw immediately that something was wrong as they were hissing at each other, screaming, had their ears flattened. I got treats out and started giving it to them which seemed to have distracted them. I then fed them, and it seemed to help even if every now and then they’d lift their heads from the bowl and hiss at each other.

          They hissed at each other throughout the evening, but went back to being friends the next day. Nowadays, 4 years later, he is chasing her, but it doesn’t look serious: he’d come up to her, starts grooming her, she tolerates it for a few moments, starts attacking him, they fight, she runs away. Sometimes he comes up to her and tries to attack, she defends herself, then runs away. At other times she starts it. It always ends up with her running away as he is much bigger.


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