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Cats/Sudden Aggression


Facts:  brother and sister, 7 years old, both fixed, both declawed front, male large and fat, female small and normal, inside cats only, access to screened porch where they can watch the wildlife (chipmunks, birds, squirrels), one litter box, one food dish, one water dish, we travel to a different city to work for a week at a time and the cats come with us and travel together in a large carrier.
Problem:  They suddenly have become aggressive to each other.  Not sure who is the aggressor.  Unable to put them in the carrier together.  They are growling and hissing at each other when they are close together around the house.  They previously curled up with each other, groomed each other, ate together at times and never became aggressive in the carrier.
Did one of them have a psychotic break?
Thank you.

This type of problem is unfortunately quite common and not a simple thing to cure.
Normally what has happened in these circumstances is that something traumatic has happened which the cats are associating with each other or one cat associates with the other. Now when i say traumatic, it can be something as simple as a fright, like a loud bang, or if one cat has been trodden on by mistake or just generally something that has frightened your cat. and for no apparant reason the cat is associating it with the other cat, strange i know, but as i say is more common that expected.
The problem is you have no way of knowing what it was that has started this reaction. All you can do is to try and get the cats to regain trust in each other again and I'm sorry to say this is a slow process. You have to go right back to step one and treat them like cats who have never met before. The process can take weeks if not slightly longer. You will have to provide the with separate everything like litter trays, carriers , feeding bowls and areas etc, because until they are happy with each other again all that will happen is confrontation and so by removing a lot of the stresses that can cause tension you will be helping the process to move along quicker. See my page regarding introducing cats to each other for further advice. /introducing-cats.html

I hope this has been useful to you.


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Kate Tilmouth


I can answer most day to day cat problems encountered by owners. I have a good understanding of cat behaviour and problems which may arise from changes to their daily routine. I can advise on cat training including litter training and general day to day cat care issues. I am not a vet and therefore cannot answer medical questions.


I run my own cat website at and have been a dedicated cat owner for over 20 years. I have encountered many different cat problems and situations and feel that i have a good understanding of cats and cat ownership.

I am a platinum member of Ezinearticles where i write mainly cat related articles.

Educated to High School level and have since worked for many years in a customer support based environment, gaining vocational qualifications.

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