What is the meaning of the highlighted phrases in this quote describing Myrtle from chapter two of The Great Gatsby by F. Scott Fitzgerald?
Her face, above a spotted dress of dark blue crepe-de-chine, contained no facet or gleam of beauty but there was an immediately perceptible vitality about her as if the nerves of her body were continually smouldering. She smiled slowly and walking through her husband as if he were a ghost shook hands with Tom, looking him flush in the eye.
Myrtle Wilson is Tom Buchanan's lover in The Great Gatsby, by F. Scott Fitzgerald. She is the wife of George Wilson and they live above his repair shop in a place known as the "valley of ashes." The Wilsons are not prosperous, and both the shop and Wilson himself are as grey and nondescript as the ash heaps around them. In the middle of all this grey dullness comes Myrtle Wilson, walking down the stairs.
The quote you cite is actually part of a longer description of her given to us by Nick Carraway, the narrator, who is seeing her for the first time:
[I]n a moment the thickish figure of a woman blocked out the light from the office door. She was in the middle thirties, and faintly stout, but she carried her surplus flesh sensuously as some women can. Her face, above a spotted dress of dark blue crépe-de-chine, contained no facet or gleam of beauty, but there was an immediately perceptible vitality about her as if the nerves of her body were continually smouldering. She smiled slowly and, walking through her husband as if he were a ghost, shook hands with Tom, looking him flush in the eye.
From this description, we sense that Myrtle is alive and sensuous in a way that nothing else in this shop--or in Wilson's life or perhaps anything in the valley of ashes--is. The word smouldering implies (figuratively) fire and heat, in this case a kind of sensuousness or sexual energy; the image Fitzgerald creates, then, is of a woman who is exquisitely aware of her body and who is sending that energy out to others.
At first it is hard to know if she is naturally this way or if something (or someone) is causing this reaction in her. No one has to wonder after reading the next line of the description; everything about her, body as well as eyes, is focused on her lover. Of course she does not literally walk through Wilson, but she is so dismissive of his presence that he does not even exist for her. He is a mere ghost, a shadow or a spot of gray, which she looks through in order to lock eyes boldly with her lover.
We learn later in the chapter that Tom and Myrtle's relationship is quite physical (in fact, Tom hits her and gives her a bloody nose), and we should not be surprised about that, given this spectacularly sensual description of Myrtle.