How does Iago manipulate Othello in Act 3?

The timing of events is very important in Act III. Iago anticipates and manipulates the other characters so skilfully that they seem to be acting simultaneously of their own free will and as Iago's puppets. For example, it takes only the slightest prompting on Iago's part to put Othello into the proper frame of mind to be consumed by jealousy. Iago exploits Cassio's discomfort upon seeing Othello by interpreting it as a sign of guilt:

"Cassio, my lord? No, sure I cannot think it That he would steal away so guilty-like, Seeing you coming."

Iago's interpretation of Cassio's exit, combined with Desdemona's vigorous support on Cassio's behalf, creates suspicion in Othello's mind even before Iago prompts him. Othello manifests his confusion about his wife by telling her that he wishes to be left alone, and by rejecting her offer of help when he tells her that he feels unwell:

"Your napkin is too little.

From the Library of Congress: TITLE: Thos. W. Keen...

Illustration of Othello and Iago

Othello and Desdemona in Venice, 1850, oil on wood...

Let it alone."

When Desdemona advocates on Cassio's behalf, she initiates the first real conversation she has had with her husband throughout the play. She also displays her strong, generous, and independent personality. In addition to his burgeoning suspicion, Othello's moodiness may also result from his dislike of Desdemona herself. Only once Desdemona has left does Othello recover somewhat: "Excellent wretch!" he says affectionately. "Perdition catch my soul, But I do love thee, and when I love thee not, Chaos is come again".

Othello seems far more comfortable expressing his love for Desdemona when she is absent. Perhaps this is because her presence makes him conscious of her claim upon him and of his obligation to honour her requests, or perhaps this is because he is more in love with some idea or image of Desdemona than...