Very Angry Cat

I have two cats, Clyde and Scooter. They are both about 2 years old, and I have had them since they were kittens. They usually tolerate each other pretty well.
In the last few week, however, Scooter has become more and more angry and agressive toward Clyde. Last night was truly the worst, Scooter viciously attacked Clyde, I was so scared that I had to break them up by throwing water on them because I thought that Scooter was going to kill Clyde.
I can't understand why he has suddenly changed in his attitude toward Clyde. Scooter gets along fine with my sister;s cats and dog, he just seems to have bad feelings toward Clyde.
Does anyone have any idea why Scooter may have changed his behaviour, and more importantly, what can be done to help prevent this.

Are they neutered?

Are they outdoor/indoor cats? If they are allowed out, is there a possible queen(female) in your area?

This is either a dominance/ jealousy thing or a mating thing. Right now my youngest, Merlin is giving everyone socks, trying to find out who's the big cheese in our house.

Try this page, scroll down the page it actually deals with agression in cats! Hope this helps!...good luck! >^..^< ! http://www.catsinternational.org/articles.html

Sounds like you have two male cats. If they are not nuetered, do that ASAP. Also, are there any stray males lurking around your house now? I had a cat for 7 years and this group of strays showed up with a big Tom. My cat started spraying all over the house and acting a lot different. Things calmed down when the stray family was gone. Also, I had to learn the hard way to recognize the dominant cat in the house. I always fed Spike first, picked him up first, greeted him first. THen he stopped "marking" on my clothes and shoes. One more suggestion: you may want to take your cat to a vet to check him out. Maybe he has something wrong that is causing him to be a meaner. Believe it or not, they put cats on anti-depressants and anti-anxiety medication just like humans. My vet told me has 20 cats on "kitty Prozac."
Good luck! Sherry

Clyde and Scooter were both neutered about 2 years ago.
The funny thing is today they are getting along better than they have in about 6 months.
I think that Scooter might just be jealous of Clyde. Scooter isn't really a cuddly cat, but Clyde is, and Clyde is always trying to sit on me or lay next to me when we sleep. It could be that Scooter is jealous of this.

Actually, I read in one of my ASPCA journals that there is a thing called "misplaced agression". If your kitties see a stray in the yard or are introduced to a new person they don't like they will stay riled up and start fighting each other!

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-Our Lady of Housecats