My cat always got that "look" before he would attack. He was always playful, but around age 10 he went batshit crazy. He viciously attacked me daily (and others too, but mainly me), unprovoked, and without mercy. He would latch on to a leg and bite and claw the shit out of me, and if i managed to pry him off, he would keep trying. He would also stalk me, and if i turned my back to him for even a second, he attcked again. I often needed antibiotics for the bites. The vet couldn't find anything physically wrong with him, and suggested I put him down. The attacks went on for over a year as I didnt have the heart to do the inevitable, but when he began attacking my young children (even clawed my infant son) I had no choice. I still feel guilty two years later. The vet said his previous health problems likely contributed to this problem, and he likely suffered brain damage from an eye/head infection he had prior to the behavior. Didn't make me feel much better though :(