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My cats suddenly fight: Is it redirected aggression from outside?

Updated On September 23rd, 2025

I have 2 cats that have been together since birth & have gotten along well. Today one started being aggressive & attacking the other. I separated them, then when they saw each other they started fighting. I separated them again all day to avoid fights. I think they marked some areas outside. Also I think an animal approached the window of the room they were in as I could see paw marks. I think the aggression is meant for the animal but is being projected on the other cat. Any insight?

2 Answers

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on April 14th, 2019

I agree! What you may be seeing is redirected aggression. The angry cat couldn't get to the source of its anger (the outside animal), so it projected it onto the other cat. I would separate the cats, and slowly reintroduce them to each other. Take the cat who is aggressive, and put her in her own room with her own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let the other cat in the aggressive cat's room while the aggressive cat is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove the second cat from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let the aggressive cat out of her room, and see how she interacts with the other cat. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep the cat in her room when you go out until they are comfortable with each other. I hope this helps!

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Other Answers

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    Answered By Jennifer Summerfield, DVM CPDT-KA

    Veterinarian, Certified Dog Trainer

    Published on May 27th, 2018

    Hi there. This is actually quite a common problem in cats. They can see something outside that upsets them, and have redirected aggression towards the other cat in the house. It often takes cats several days to calm down once they've gotten worked up like this. Your best bet is to separate the cats for now, to give Lila a chance to calm down before slowly reintroducing them. The more she continues to hiss and growl at Gracie, the worse this will make things - so it's important to get them separated to prevent this from becoming a long-term problem. I would wait at least a week or two before trying to gradually reintroduce them. See our article on introducing a new cat to the household for more information on how to manage this. The same process will work for two cats who are being reintroduced after a separation: https://www.petcoach.co/article/5-steps-to-introducing-your-cat-to-a-new-feline/

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