Juliet writes to Sidney. She's distraught because he recently sent Isola a book on phrenology, which Isola is taking very seriously. Isola has insulted several neighbors. The one good thing to come of this is that, at supper last night, Isola was inspecting Eben's head and Remy was unable to contain herself—she burst out laughing. Juliet mentions that she and Dawsey are awkward around each other now.
Phrenology, or reading one's head for personality clues, is entirely baseless. Isola's seriousness about it then suggests that she's not particularly critical when it comes to what she reads; if it's in a book and is interesting, she'll take it as fact. In this case, this actually deprives her of connections.