I just can't see how it can happen as you just described. If he's dragging his feet, the nails are pointed away from the skin and there is no pressure on the sharp tip of the nail. I wonder if you aren't allergic to something on his feet. Or maybe he is grabbing your arm hard when you try to remove him from your arm and you are pulling him off your arm. Skin, (unless you have some kind of skin disease/condition) is just not so fragile that it is damaged with no pressure, even with something very sharp. I can understand puncture wounds happening when you are handling them correctly, but not a scratch.