gaining on a kitty.

as many of you guys know of my story and how i came to have 5 cats. ok now i have a new type of weird behavior, my youngest cat squirrel gets picked on by the others and we dont know why. they chase her and hiss at her. this started up almost a week ago. they havent been broken up or anything they stay in the household and never go anywhere. they are strictly indoor cats. has this happen to anyone?

Cats will turn on a cat suddenly if they sense that they are sick. If this happened in my household, I would take the one being picked on to a vet.

I have a cat with chronic urinary issues and I know when he's starting to flare up by the behavior of the other cats towards him. At least 2 of them pick on him.