Early on in their friendship, during their college years, Kristen and Emily invented a secret coded language that only they share. The code has no one-to-one system by which certain letters or numbers equal other letters or numbers; instead, the code operates on the assumption that each woman will be able to detect patterns the other woman creates in a written message. The language also draws on the idea that each woman knows the other so well that they will be able to notice words or phrases that the other would never usually say, and therefore realize that those words or phrases are essential to unlocking the code.

On one level, this code demonstrates the friends‘ closeness. Their friendship has a childlike quality, a desire for exclusivity and an intimate circle no one else can enter. When the reader learns that Kristen is probably somehow trying to use Emily as a replacement for her childhood best friend, Jamie, the friendship’s intensity becomes even more understandable.

On another level, the code demonstrates that Kristen and Emily have uncannily similar thought processes. The similarity in thinking patterns that the code sometimes requires strains the boundaries of verisimilitude; it seems almost impossible, in other words, that one friend could pick up on the subtle clues that the other friend leaves in the code.