After reading this poem for the first time, I caught a few themes being presented in this poem: power associated with having this feminine body part, lack of male siblings, comparison to society's standards, as well as the "solution" to the narrator's sexual lust.
The power with which this body part is regarded by the narrator is caught in the first few lines: "the key to everything." To this statement, in what scope of things does Sexton refer to "everything"? However, I believe this question is answered throughout the rest of the poem, the breast standing for the key to controlling men. Growing up with her sisters, the narrator had to figure this out on her own, not having heard these news from possible male siblings. The narrator figured something was missing when comparing herself to society's top standards, that of movie stars. This is an interesting theme to bring up because it is often not talked about aloud: the envy one has for another person's advantage. It is more commonly thought in one's mind.
Another thing I found interesting about this poem is that though the narrator speaks of her maturing, the progress in the description of herself lacks does not follow. "Playthings" and "snail" sound equally as vulnerable and yet, this is supposed to show how she matures. However, this might be a reflection of how the sexual lust is still similar to that of young girls, leaving Sexton to end off her poem with a provocative phrase: "I burn the way money burns." This statement may be an analysis of how she is still at the whims of her lust, as money is not "burnt" (spent) through it's own doing, but that of the possessor.