Act 4 Scene 1
Iago continues to torment Othello with vivid descriptions of Desdemona’s alleged sexual activity until Othello blacks out. Iago then places Othello where e can see (But not hear) a conversation with Cassio about Bianca, telling Othello that the bawdy conversation is about Cassio and Desdemona. Othello’s fury grows.
Lodovico arrives from Venice with orders from the duke and senators that Othello return to Venice and that Cassio be appointed in his place. Othello strikes Desdemona in Lodovico’s presence, then rudely dismisses her, and leaves in a jealous rage. Lodovico expresses his astonishment at the change in Othello.
Act 4 Scene 2
Othello questions Emilia about Cassio and Desdemona’s relationship, acting as if Emilia is the mistress of a brothel and Desdemona one of her prostitutes. Othello denounces Desdemona to her face as a *****. Desdemona turns for help to Iago, who reassures her.
Roderigo, protesting to Iago that his gifts to Desdemona have won him no favor from her, threatens to ask for the return of the gifts. Iago counters this threat by telling Roderigo that Desdemona will leave for Mauritaia with Othello unless Roderigo can delay them. The best way to do this, says Iago, is by killing Cassio.
Act 4 Scene 3
Othello, walking with Lodovico, orders Desdemona to go to bed and to dismiss Emilia. As Emilia helps Desdemona prepare for bed, they discuss marital infidelity, with Desdemona arguing that no woman would be unfaithful to her husband and Emilia arguing that women have the same desires as men do.