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 whore. 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 Mauritania with Othello unless Roderigo can delay them. The best way to do this, says Iago, is by killing Cassio.