There is no set time for cats to get along. A kitten can come into a home with another kitten and they are getting along within an hour. Two older cats who have had bad experiences might take a year.
But most cats can get along. The cats who don't get along are marked "Only Cat" in the shelters. These are usually cats who were raised away from other cats, and are too nervous to change that attitude.
We can't tell if we have an only cat, though if we raised them from a kitten that's unlikely. A cat usually has to have a bad experience with another cat to develop an aversion.
The first thing we should do with two cats who don't get along is put the cat who seems to be the most aggressive about it into their own separate room. They want to be the boss of everything. Having their own room will let them be the boss of everything... in that room.
We must never hit or yell at the cat.
This only teaches the cat to be afraid of us.
The cat who has been attacked most often will relax and gain confidence. They can go through their cat routines without looking over their shoulder.
This should also stop the cats using our stuff as a bathroom, ripping things up, and trying to hurt each other.
Once we've had some peace and quiet, we can let the aggressive cat out of their space, but first see how they are handling the space.
If they are pacing and howling and generally acting unhappy, we know they are high energy cats, and need a lot more play than we have been giving. We will give them more play sessions and try to wear them out. We will get out the water bottle and shake it when they try to make trouble. If that doesn't work, only then we can squirt them.
If they make an effort to get along, we won't be as quick to put them in another room as we would if they immediately start stalking their victim again.
If they are bouncing around playing and happy, and immediately try to play with us when we come in, that is all they were trying to do with the cat who got mad at them. The other cat is just too quiet or too old to play as much as the other cat wants. And this won't change.
We should probably get the rowdy cat a kitten to play with. Having three cats who get along is a lot better and easier than having two cats who fight.
If they are lying around and acting relaxed, this means they are not cats with an aggression problem. They are cats who were so nervous with the other cat or cats, the activity in the house, the dogs or kids or noisy stereo that they couldn't think straight. Something was making this cat nervous and touchy that is no longer there.
We need to make a quiet space for this cat, just for them, and not let the other cats bother them there. In turn, this cat is unlikely to run around and get in the other cat's space.
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