When seen in connection to the dumpster and the night, the "open and shut" reference also makes more sense. The dumpster opens when something is thrown in, and shuts again to keep the garbage or the smell from escaping. The smoker opens his or her mouth and lungs for the smoke to enter, and closes down to enjoy the effect of the smoke. Open and shut could refer to the smoker's eyes. The smoker opens his or her eyes in order to see the cigarette and light it, and closes them in order to experience the pleasure of smoking more fully. In combination, the two parts of the sentence "All down the block something inside you opens and shuts" then refers to the mental process of the smoker while in the throes of enjoying the cigarette. The person as it were travels mentally to the dangerous night on the wings of the smoke that escapes the room. He or she opens and shuts to the experience and to the addiction: opens to let it in, and shuts to keep it inside, not wanting to let it go. This is substantiated by the opening line: "Who would want to give it up..." - certainly not the smoker.

The entire poem is filled with this type of juxtaposition: smoking is both beautiful and dangerous; it provides the illusion of safety even while it kills. The smoker is fully aware of death lurking both outside and inside the body, ready to pounce at some inopportune moment. The poem is almost as filled with death symbolism as it is with the beauty of the smoke that brings it about.

The "rasp" of the smoker's breath contrasts...

Like the smoke, the rasping breath grows lighter and lighter until it is finally thin enough to cease existing. The smoky "fingers crawling the pale stem of your neck" also signifies death in a very visual and somewhat horrifying way. The images solicited by diction such as "crawling" and "pale" are of corpses and crawling insects in the grave.
And indeed, right after these grisly thoughts, the poet states directly that "Death's shovel scrapes the sidewalk, critches across the man-made cracks...." In this and the following lines the poet graphically personifies death, juxtaposing "him" not only with the recently mentioned idealized beauty of death, but also with life and humanity. The poet appears to indicate that death is not only inevitable, but also above all else in the natural and artificial world; it ravages and eventually claims everything. This is the danger of addiction.

Still, knowing this fully, the smoker continues his or her habit, unable to "put out" the light at the end of the cigarette, because the night inside is already to far advanced to ever give way to living again. As such, the smoker become the living dead, holding onto life only by the flimsy tendrils of the smoke for which he or she gives thanks, because it is death, but it is beautiful even in its brevity, and exactly because of its brevity.