What's Gotten Into Bubbles

Bubbles, the year and a half old calico I took in was getting along nicely with Sophie and the cats until a couple of weeks ago. All of a sudden while rubbing up against Sophie she'd get mad because Sophie wouldn't stay put and then she'd turn on Sophie and give her a swat on her nose. Then last weekend Bubbles bit Sophie on her face and the attacks escalated. I kept a close eye on Sophie and while she stayed clear of Bubbles, Bubbles would seek her out and attack. Barb is arranging for one of the other foster moms to take Bubbles as I want her out of the house as soon as possible.