When Desdemona re-enters, Othello's aspect is changed; he watches her intently, looking for signs, and brushes away her handkerchief when she seeks to sooth him. They go in to dinner, and Emilia picks up the fallen handkerchief, one that her husband, Iago, often urged her to steal from Desdemona. Emilia decides to have a copy made to give to Iago, but he enters, sees the handkerchief, and snatches it from her.
When Othello enters, Iago sees that Othello cannot regain his peace of mind. His speech is fevered, sweeping and frantic; he believes that his wife has been unfaithful to him. Othello then turns on Iago with savage intensity and demands to see the proof of Desdemona's infidelity. Cornered, Iago produces the dream story: Cassio spoke in his sleep, embraced him, called him Desdemona, and cursed the Moor. Iago tells Othello that he has seen Cassio wipe his brow with a handkerchief embroidered with strawberries; Othello recognizes this handkerchief as the one he gave to Desdemona.
Othello dismisses love and calls for vengeance. Certainty has freed his mind from doubt and confusion. Now he swears action, and Iago swears to help him. Othello wants Cassio dead, Iago agrees to do it, and then Othello wonders how to kill Desdemona.
