We're trying to introduce Lucena, a 1 year old shy Siamese female kitten, to Elsa, a 3 year old extrovert Siamese female cat, living with us in our apartment since two years. Both are spayed.

We noticed Elsa tends to be very aggressive with new cats, so we're trying to introduce Lucena slowly. At the moment Lucena stays in a study room behind closed door, to keep her out from Elsa. Once-twice a day we let Lucena out to explore the rest of the house while locking Elsa in the study, so she can know Lucena's smell.

Three weeks went by, and one particular behavior by Elsa seems to be constant: she spends lots of time, sometimes an hour, focused and looking at the bottom gap of the closed door, with directed ears and the tail sweeping left and right against the floor. During that time she seems mostly unaffected by our calls, toys, laser or food. When we enter the room, she always tries to enter as well. And after Lucena has her time outisde and Elsa is back, she looks suspicious and walks around the same spots Lucena walked before. It's like she's tracking her smell.

On the few occasions they physically met by mistake (five times so far, last time yesterday), Elsa attacked Lucena with no second thought. Fur and spit were on the floor, and we had to separate them immediately.

A tip I read often, is to let the cats eat at opposite sides of the door to let the other cat's smell be associated with positive things. We started doing that a few days ago, and after the first few meals Elsa does indeed eat almost continuously (except stopping for a few seconds while hearing crunching sounds from the other side of the door), but few minutes later she's back at guarding/patrolling the door.

Is this behavior normal for a cat getting to know a newcomer? Or is it something we should be worried about? Any actions we should take before proceeding to let them eat with visual, non physical contact?

  • Does she seem curious or angry? It sounds like the latter to me, but I'd expect the former after having 3 weeks to accept the new cat's scent as a normal part of the territory.
    – StephenS
    Jul 4, 2020 at 16:58
  • Hard for me to say. Her tail is usually not as thick as when she's angry, although we briefly saw her with a thick tail today. Jul 4, 2020 at 17:13

1 Answer 1


The behaviour you describe is normal for a cat that does not want the other cat in her territory. If your old cat has made up her mind about the other cat, there is very little you can do.

That being said, please do not give up; there is a chance your oldest cat only wants the other cat to know that she is the boss. A lot will depend on the new cat and how she reacts to the older cat's aggression; your new cat might stand up for herself and the situation might solve itself.

You can expect hissing but this is most often only a warning to the other cat to keep the distance; however, it is a warning and you need to take it seriously.

You need to know that the situation might end in violence where one or both cats might get hurt; you need to provide both cats a route of escape, preferably a couple of elevated areas where the cats can be relatively safe from each other.

When the two cats meet face to face the first time you will need to have somebody with you so you can have control over both cats; this is dangerous for both people and cats, so please be careful.

If everything fails, you will need to find a way to rehome the young cat; I hope you can avoid this option.

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