The pebble is used symbolically to suggest fidelity or the loss of it. We’re first introduced to the symbol by Thomas, when he talks about the courtship rituals of penguins. The pebble is a gift from the male penguin to his chosen, lifelong mate. The meaning of the pebble changes over the course of the book. First, it’s an indicator of Thomas’s love for Alice. Later, a pebble necklace becomes a clue in Virgil’s search for hard evidence.

We are told that Alice wears a pebble necklace that she never takes off. The reader naturally assumes that the necklace was a gift from Thomas. However, when he sees Jenna wearing the necklace, Thomas views it as a sign of betrayal and slaps her. We later learn that it was actually a gift from Gideon to Alice as a sign of his fidelity. It might also be viewed as a symbol of Alice’s fidelity toward Jenna. The girl interprets it as a message from beyond the grave. It’s a sign that her mother wants to be found.

A dollar bill folded into the shape of an origami elephant is another symbol first introduced by Thomas. He uses it to defuse his tense initial relationship with Alice, and it continues to perform this function throughout the book.