Cannibalism is the main symbol of this novel, because it is fantasies about cannibalism that finally return this married couple to some intimacy. Intimacy issues are embarrassing and difficult to explain, and as the novel notices toward the ending, honesty is a major factor in that question. If a person harbors secret feelings about their partner which they feel unable to share without harming the other person, then whenever they try to connect romantically, their hesitations will prevent them. So, if the reader can discover what cannibalism secretly means, they will see an argument unfolding about human connection.
The argument is simple: Human romance is often done as an act of self-nourishment. In other words, accepting someone's time and affection is a simple way of experiencing emotions that are hard to give one's self. The novelist depicts this self-centered, easy, lazy kind of love as cannibalism. Interestingly, Olivia tells her husband something that he doesn't want to hear, then he imagines her eating human flesh, and suddenly, he is aroused. That means that he is intrigued by the femme fatale—he is caught up in self-esteem issues. Without knowing his value as a human, he finds himself limited by Olivia's affection.
Since Olivia is an extremist at heart, while her husband is more thoughtful and less impulsive, Olivia is bored by him. This, along with the cannibalism, set up a self-esteem dilemma where the husband must assert himself. She likes that he defends himself, and the honesty makes is refreshing, so that when the husband decides to perceive Olivia as a cannibal, he is able to connect with her. One interesting conclusion here might be that secretly, his personal vendetta against his wife comes from the fact that he knows her relationship to him is essentially ego-centric—like a cannibal who eats humans for sustenance, Olivia is a wife who eats her husband's time and attention, and when he is honest about that, then they can connect again.
