In a passage marked with hyperbole, Mr. Lisbon reflects with surprise on his inability to truly understand his daughters, whom me metaphorically compares to "strangers":
Apparently, as he stepped back inside, he saw Therese come out of the dining room [...] Her high forehead glowed in the light from the street and her cupid’s lips were redder, smaller, and more shapely than he remembered, especially in contrast to her cheeks and chin, which had gained weight. Her eyelashes were crusted, as though recently glued shut. At that moment Mr. Lisbon had the feeling that he didn’t know who she was, that children were only strangers you agreed to live with, and he reached out in order to meet her for the first time.
Earlier, the neighborhood boys help to scrape dead bugs off the side of the Lisbon home, as Mr. Lisbon has stopped taking care of his house and yard following the suicide of Cecilia. However, the boys motives are not quite pure, as they take advantage of the opportunity to observe the Lisbon sisters from the windows. They watch as Mr. Lisbon encounters Therese and suddenly realizes that "he didn't know who she was." Though this is certainly a hyperbolic claim, there is also some truth to it. Though he lives with his daughters and seems to care for them, he does not truly know them, and was unable to predict Cecilia's suicide, which remains a mystery to him. He feels, suddenly, that "children were only strangers you agreed to live with." Though this claim is both hyperbolic and metaphorical, as Therese is by no means a stranger to her father, it again reflects his sudden awareness of the difficulty of truly knowing what other people are thinking or feeling, including those close to him.
Eugenides employs a simile and an extended metaphor in order to express the widespread belief in their hometown that Cecilia's suicide was akin to an infectious disease that ultimately spread ot her sisters:
Already Cecilia’s suicide had assumed in retrospect the stature of a long-prophesied event [...] Her suicide, from this perspective, was seen as a kind of disease infecting those close at hand. In the bathtub, cooking in the broth of her own blood, Cecilia had released an airborne virus which the other girls, even in coming to save her, had contracted. No one cared how Cecilia had caught the virus in the first place. Transmission became explanation [...] Spiky bacteria lodged in the agar of the girls’ throats. In the morning, a soft oral thrush had sprouted over their tonsils.
When Lux feigns a burst appendix in order to visit the hospital and take a pregnancy test, she meets with Dr. Hornicker, who had previously met with Cecilia after her suicide attempt. After the other sisters commit suicide, Dr. Hornicker advances a theory that Cecilia's sisters suffered from PTSD, or post-traumatic stress disorder, following Cecilia's death. Many in the neighborhood come to think of Cecilia's suicide "as a kind of disease," a simile that reflects their desire for a scientific explanation for these otherwise inexplicable acts.
Further developing this notion through an extended metaphor, the neighborhood boys state that, in the local imagination, Cecilia "released an airborne virus which the other girls, even in coming to save her, had contracted." Nobody can ultimately explain "how Cecilia had caught the virus in the first place," but they are satisfied with their conclusion that she was the source of the infection, which quickly spread to her sisters. Ultimately, this language of illness, viruses, and bacteria reflects one of many attempts bye characters in the novel to "solve" the mystery surrounding the sisters' actions.
After the deaths of all the Lisbon sisters except Mary, Mr. and Mrs. Lisbon decide to sell the family home, hiring Mr. Hedlie, a school-teacher, to clean and remove the hoard of useless objects left in the home. Using a metaphor, the neighborhood boys compare the sudden rush of objects, from trash to personal mementoes, to a “tidal wave”:
But despite all this new evidence of the girls’ lives, and of the sudden drop-off of family togetherness (the photos virtually cease about the time Therese turned twelve), we learned little more about the girls than we knew already. It felt as though the house could keep disgorging debris forever, a tidal wave of unmatched slippers and dresses scarecrowed on hangers, and after sifting through it all we would still know nothing. There came an end to the outflow, however. Three days after Mr. Hedlie forged into the house, he came out, opening the front door for the first time [...]
For years, the neighborhood boys have treasured any small mementos associated with the Lisbon sisters, with whom they are obsessed. Now they feel overwhelmed by “all this new evidence of the girls’ lives” when Mr. Hedlie begins to remove the family’s personal effects, including family photos and clothing. They note that it “ felt as though the house could keep disgorging debris forever, a tidal wave of unmatched slippers and dresses.” Here, they somewhat hyperbolically imagine a flood surge of objects exiting the home, describing it as a “tidal wave.” This metaphor underscores just how much the Lisbon family had hoarded in its year of isolation and highlights the boys’ excitement, as they suddenly know far more about the minor details of the girls’ personal lives, information which they prize.