Synopsis:
Northwest takes her in and plans to move on shortly, so she'll need to hunt down new digs. When he asks her questions, she is evasive, cagey. He doesn't pursue questioning, in favor of her right to privacy.
He starts to have weird dreams of snakes wrapping around him.
Analysis with Spoilers:Of course, the dreams are real. She has been cagey about what she lives on because she lives on humans. Humans are victims who are willing (if not consciously), ecstatically enthralled, and unable to break the spell. A friend, dropping by, finally frees him.
There are a number of fascinating aspects. Probably the first and most obvious point is its nearly overt sexual nature. I suspect this accounts for its initial reprintings: men captured, enthralled by their baser natures. This parasitic race sneaks into their lives, and suddenly what once seemed innocent becomes an entirely different creature.
This enthralling (note the passive sentence construction) builds an inherently passive story structure. While the protagonist acts at the start, his acts dwindle. It isn't that dynamic a narrative. This may account for its not being reprinted that often in its first fifty years (do note, however, that story was popular enough to be recorded on l.p.--see Youtube readings by the author). Suddenly, in the 90s and 00s, it gained respectability. Maybe the reason is that it requires rereading to tap into its power. Still, it's fascinating that a passive construction works so well.
Perhaps it should be enough to say she mined the puzzling nature of human sexuality. But that isn't all. This also maps on to human addiction. Things have a way of asserting control over our lives. We let something into our house whose nature we were unfamiliar with, and we find ourselves mired in a stupor, be it drugs, social media, Twinkies, or whatever has us in its thrall. Northwest is commanded by his pal to kill the Shambleau should he ever come in contact with another alien like it. The beautiful and haunting final lines of "I'll try" said in a wavering voice hint at the fear that one can never be free of one's addiction.
Presumably a case could be made for this tale being racist since she is brown-skinned and wears a turban. But it would be a lazy, partial reading, ignoring first that apparently that turbans are fashionable in this time and place, second that Moore needs the turban to hide the Medusa snakes, and third that such a reading blindfolds itself to the whole story and its broader scope, It's like watching a trailer and judging the film's merit from that (sometimes it works, but that may be chance or some other factor. That said, it often seems like a movie is bad if the trailer cannot hint at the movie's arc). Of course, a reader can read however they choose to, but if it doesn't account for the body of work, it probably maps the reader's own mind, rather than the story.
The prologue is a kind fascinating snapshot into the writer's mind. It feigns to make grand claims about humanity while both hiding and showing her hand that this story explains the myth of Medusa in a future setting, suggesting humanity had been to the stars earlier and the tale of Medusa is just a racial memory of that alien encounter.
A wonderful feature of this tale is that Moore allows this to be a story first, to follow that story no matter where it leads, and to hang willingly in those gray ethical zones. Today we'd too quickly deconstruct Shambleau to represent female sexuality which must be protected, ignoring the parasitism involved (which is a huge chunk of story--also it said that some Shambleau represent themselves as male). Rather, this pits one's desire for life against one's desire for the thrill that can kill them: narcotics, fried chicken, martinis, sex--whatever slakes your thirst for delicious poison.