De Beauvior's premise is that sex, for women, is always about becoming "prey" for the man. Sex is always about the objectification of women by men; men are "active" in that they seek to penetrate the woman; women are "passive" in that they are receptacles for male desire. In this way all sex is a kind of rape; women, by virtue of their anatomy, are required to undergo violation.
De Beauvoir traces how this objectification is manifest in the psychology of women, with sections dealing with the awakening of desire, loss of virginity, and frigidity. There is a kind of doubleness in feminine sexuality that comes from, on the one hand, the clitoris as the center of sexual pleasure, and, on the other, the vagina as the center of biological reproduction. Perhaps the most memorable section of the chapter, if one can be singled out, is her attempt to distinguish the nature of feminine sexual pleasure from male pleasure. Male pleasure is finite, and has a definite, and biologically significant, end: ejaculation. Female pleasure, however, can take many forms, she argues; a female orgasm is much more indefinite, and the female urge, far from reaching a final goal, as in the male, is rather to achieve a kind of infinite, suffused pleasure.
She concludes by saying that what women envy in men is not, as Freud thought, their penises, but rather their "prey," the power to objectify others. This is perhaps the most significant observation in the chapter; it suggests that while male autonomy is a result of their sexuality, for women this autonomy must be gained in spite of their sexuality.