I have an adult boy cat. This just started... about a year now, when I touch, scratch or even just rub my hand down my cats back he immediatly starts to knaw on his paw. I dont know why? He stops when I stop. But here recently my young girl cat is doing the same thing when I touch,scratch or rub the tip of her back by her tail only. I have changed the food bowls to glass bowls, changed the food to a different brand, changed the kitty litter brand, and moved to another apartment in a whole new location. Im not sure what else to do. No, they are not on any medications or flea meds. So what can I do to make him go back to letting me pet him normally again??