Suddenly aggressive kitty

Question
I hope you can help me! I have two kitties, my female is about 6 years old and the male is 4 or so. They've lived together almost incident free for the last 4 years but for some reason last night she turned hostile towards him. Hissing, growling, swatting..it's really bizarre. They've always play fought but never anything agressive like this.

The only thing I can think is that my neighbours cat across the hall is causing this disention, it howls almost constantly (either outside to be let in, or inside and lonely I'm assuming) I'm not sure what to do to calm her down! Any help would be appreciated!

Answer
Epiphany,

That is normal reaction that is called "Redirected Aggression". She is probably taking the neighbor cat's howling as a threat but she can't get to him to protect her territory so she is turning to your other cat and is behaving toward him as she would the cat out the door. If the cat is a tomcat (not neutered) then she could also be having the same reaction from that. She is not actually attacking your other cat....in her mind she is attacking the outside cat.

The best thing to do is to put her in a room by herself when she gets like that to let her calm down. I would also speak to the neighbors. They may not realize what their cat is doing and how it is upsetting yours.

Maybe you can let their cat in and let him get to know your cats. It would help his loneliness, quiet him down, and calm your cat (maybe!). Or put up some type of screen where your cats can see this 'threat'.

Tabbi