You start to see in it premonitions of her suicide. The title suggests being on the edge or having slipped off it. Since the poem is about a "perfected woman," one starts to read it as the poem about Plath herself dead, perfect. The central figure then becomes the woman Plath thought she would become by her suicide, with the relief and defiance, the all-encompassing knowledge ("she is used to this sort of thing") she would then possess, as well as her frightening qualities ("blacks crackle and drag") that, in her superior way, she can take for granted, although we, the reader, cannot.