My son loves a cat in our building. The cat rolls on its back and stretches out, and my son strokes his fur. But then he tries holding the cat with both hands, sometimes around the waist (the cat steps out) and sometimes the cat's head. He gets more bold the longer they play, and I usually get nervous and intervene while the cat still seems happy.
How can I determine if my son is doing something that will hurt the cat, make it afraid, or make it bite/scratch him?