WHY ARE MY CATS FIGHTING ALL OF A SUDDEN?

If your cats start hissing and clawing out of nowhere when they used to be friends, you might find yourself wondering, "Why are my cats fighting all of a sudden?" What was once a happy friendship has now turned into bullying and flying fur. Whether they're fighting because they smell differently or got spooked, your cats probably won't stay enemies for long. Here are some reasons why your cats don't get along anymore, as well as steps to help ease them into a friendship again.
Fear Takes Over
Sometimes cats get scared, and this causes them to misdirect their "fight or flight" response at the wrong target. This might happen if two cats are sleeping peacefully next to each other, then hear a loud noise. Both cats get scared, jump, and puff up into defensive postures. They see each other puffed up and fear the other is attacking. This could lead to unease and fighting until they figure out they're still friends.