It seems that the phrase "thick with birds" is literal, since Sula returns to Medallion "Accompanied by a plague of robins" (1937.1). The birds are everywhere, and the townspeople recognize them as "the legitimacy of forces other than good ones" (1937.4).
Sula arrives amongst this plague of birds, "dressed in a manner as close to a movie star as anyone would ever see" (1937.5). She heads straight to Eva's, and when she enters the house Eva tells her, "I might have knowed them birds meant something" (1937.8).
The two women have a nasty exchange. Eva chides Sula for not keeping in touch. Sula accuses Eva of purposely losing her leg and tells her "to shut [her] mouth" (1937.27).
Then Sula brings up Plum's death and Eva's role in it. Eva fires back by accusing Sula of standing by while Hannah burned in the backyard and tells her that she is "the one [who] should have been burnt" (1937.38). Sula declares that she's going to be the one starting "Any more fires in [the] house" (1937.39), threatening to set Eva on fire the same way Eva set Plum on fire.
Eva takes this threat seriously and starts sleeping with her door locked. And while Sula never sets Eva on fire, she has her committed to a nasty mental hospital just to get her out of the house.
The chapter shifts to Nel at this point, who senses a change in the air now that Sula has returned. She loves that "her old friend ha[s] come home" (1937.55), calling it "magic" (1937.55). Their friendship picks up where it left off; Sula hangs out at Nel's in the afternoons, and they laugh and reminisce about their childhood.
Talk turns to sex, and the two women wonder why they ever made such a big deal about it. They laugh about a guy named John L. who tried to have sex with a girl named Shirley by "tr[ying] to stick it in her hip" (1937.82). The laughter they share makes Nel "[feel] soft and new" (1937.102).
Nel asks Sula about her years in college, but she doesn't seem to share much. She does tell Sula about committing Eva to Beechnut (the mental hospital), and Nel is completely shocked. She tries to understand why Sula would do something so horrible, and Sula tells Nel that Eva frightens her. (We know this isn't true since we get to witness the nasty fight between the two women.)
Nel realizes that Sula hasn't changed, that she is still "incapable of making any but the most trivial decisions" (1937.153), and that "when fear struck her, she did unbelievable things" (1937.153).
As the practical one, Nel tells Sula that they'll figure out how to make sure that Eva doesn't get mistreated at Beechnut, and she reassures Sula that "It's going to be all right" (1937.167).
Jude gets home from work after a horrible day. He tells his wife and her friend that black men lead hard lives. Nel is ready to comfort him, but Sula chimes in and disagrees. This angers Jude at first, but then Sula explains herself.
She declares that "everything in the world loves [black men ]" (1937.176) and then offers some examples that are a little strange. She comments that white men's desire to "cut off a n*****'s privates" (1937.176) and white women's constant fear of being of being raped show how much they love black men. The fact that, "Colored women worry themselves into bad health" (1937.176) about how to hang on to black men shows their love. She also states that, "Nothing in this world loves a black man more than another black man" (1937.176). For all of these reasons, Sula decides that, "It looks to [her] like [black men are] the envy of the world" (1937.176).
This makes Jude laugh, and while he decides that Sula isn't physically attractive, he can see how she could "stir . . . a man's mind maybe" (1937.177).
And then something horrible happens. Nel walks in on Sula and Jude having sex in her bedroom (1937.180). Sula never looks at her or even tries to cover up, and she doesn't seem particularly sorry. As Jude gets dressed, he looks at Nel the same way the soldiers on the train looked at her mother all those years ago. As Nel tries to make sense of what's happening, she suddenly thinks about how messy the bedroom is and how she wishes she "had gotten the dust out from under the bed because [she] was ashamed of it in that small room" (1937.181). Jude brushes by Nel and all he says is, "I'll be back for my things" (1937.181).
After Sula and Jude leave, Nel tries to find a place for herself in the house to think. She wants a "very small, very bright place" (1937.183), so she locks herself in the bathroom and sits on the floor.She starts to think about Chicken Little's funeral and about the women who were overcome with grief. She used to think of them as exhibiting "unbecoming behavior" (1937.183) with their screaming and crying, but now she realizes that they were simply responding to "a simple obligation to say something, do something, feel something about the dead" (1937.183).
Since Nel's marriage to Jude and, more devastatingly, her friendship with Sula have all but died, she keeps expecting to scream and cry the way the women did at the funeral, but it never happens. Instead, she begins to feel "a flake of something dry and nasty in her throat" (1937.188). Then she spots something in the bathroom: "a ball of fur and string and hair" (1937.189) hanging in the air.
We're not sure what this ball signifies, but we can assume that it is all in Nel's imagination and that it is a way for her to somehow deal with her grief. She continues to see it, and it disturbs her so much that she starts sleeping with her children.
Nel starts to think that if she were ever to touch the ball she might die. Then she decides that this might not be so bad, since dying "was sleep and there wasn't no gray ball in death, was there?" (1937.189).
Nel wants more than anything to be able talk to Sula about this, to ask her what she thinks about death. We realize that, while Nel is sad to have lost Jude, losing Sula has been worse. It's clear that most of her grief is for the loss of her friend.