A few people are born with a rare disorder that prevents these people from feeling pain.
Is "hurting" these people - i.e. doing to them things that would cause others to feel pain but don't have much of an effect on these people - just as morally significant as hurting people who do feel pain? (Let's assume there are no long-lasting injuries involved.)
I ask not because I want permission to hit people, but because I wonder how closely related pain as a neurological phenomenon is to suffering as a moral phenomenon.