My Grandfather thinks feeding the 3 cats massive amounts of food is fun. He must gain pleasure by watching their bodies inflate like balloons. He gets the blue ribbon for fattest cats.

This is what I'd have fun doing with the cats:
Paint little targets on their foreheads with red nailpolish and try to hit the bullseye with rubber bands. (Yeah, that might actually be cruel, but the vomit/urinate in the house and while my grandparents don't mind, I find the odor embarrassing. Though I only need to live there 2 more months, they give me serious allergic reactions. So they are cruel to me. Besides, I'm not killing them.)