I used to think the way to punish a confessed masochist (to impress on the other that you're the one in power) were to make sure the level of pain gets in the overkill lane in relation to the "crime" and keep jacking up that level, at least change the level ("even if you're obedient to me you're not obedient enuff, bitch") but it's not that simple...And if you actually want to change the behaviour of the sub (make her stop smoking) that wouldn't be the good way. Writing an essay sounds better.