Dom Casmurro names Othello, the tragedy in which a general kills his wife out of jealousy, and uses it as a mirror. Bentinho gives the title "A Touch of Iago" to the chapter in which a phrase of José Dias awakens his first jealousy, proposes in chapter LXXII that plays begin at the end, and in chapter CXXXV goes to the theater to watch Othello, which he "had never seen or read."
In the play, the spectator knows that Desdemona is innocent, and the tragedy lies in seeing Othello err. Bentinho leaves the theater with his conclusion formed, not with doubt: he concludes that "not I, but Capitu must die," and asks what the audience would do if Desdemona were guilty, "as guilty as Capitu."
The novel departs from the model at the decisive point. In Shakespeare the certainty of innocence is given to the spectator; in Dom Casmurro that certainty is never granted, and the reader does not know whether Capitu is innocent. Moreover, Othello's proof is a handkerchief, while Bentinho's is the resemblance between the face of a child and that of a dead man. The next morning comes the scene of the coffee cup.