Since there seems to be some confusion about certain words, here is the explanation I gave in the comments. The whole poem is essentially one continuous line/thought. On her velvet lips, that are reddest at night, before the slips (slips referring to slips of tongue, much like you would say with a term like 'Freudian Slip') of careless slight (slight meaning an insult) there plays a smile that grips my heart tight and strips of me of each right I have.