Act 4, Scene 1 Summary

Othello and Iago discuss the straying handkerchief and the sins it might imply. Iago casually mentions the idea of Desdemona being naked in bed with Cassio, then backpedals in his very next breath. Othello says that the missing handkerchief is insufficient proof of guilt. Iago then pretends that he actually overheard Cassio boast of his escapades with Desdemona. This comment succeeds in working Othello into such a state that he enters a sort of trance. It's almost as though he's truly bewitched, poisoned by Iago's words.

Cassio enters. Iago informs him that something is not quite right with Othello, but that if they let it run its course, he will be fine. He urges Cassio to leave, but to come back shortly to talk. When Othello emerges from his trance, Iago brings up the subject of infidelity immediately. Othello is undone...