She suggests that one put their name and phone number on a $5 bill and the other on the front endpaper of a book that will be sold the next day. If each finds the other's item they are meant to be together, and can make contact. The book that Sara writes her number in is Gabriel García Márquez's "Love in the Time of Cholera". This is a significant symbolism, because in the book, the two protagonists met while very young and their love was forbidden until they were reunited in old age.