The principal method that Iago uses to convince Othello of Desdemona's infidelity is by using one of Othello's most treasured possessions and telling Othello that his wife, Desdemona has given it away to her lover, Cassio. This treasured possession of Othello's is a handkerchief, which "Did an Egyptian to my mother give". The handkerchief is important to Othello because it is a link back to his mother who also told Othello to give it to his wife. "She dying gave it me, And bid me when my fate would have me wive, To give it her". So to Othello this handkerchief is very important, especially as he describes it as having "magic in the web of it". It was also the first gift he gave to Desdemona, so this handkerchief is of enormous sentimental value to Othello. Finding out that Desdemona has given it away without a care for him, would almost certainly anger him, for in Othello's mind she has thought the handkerchief to be a meaningless piece of cloth. Iago tells Othello that he saw Cassio wiping his mouth with it, much like a rag. " I know not that; but such a handkerchief- I am sure it was your wife's- did I today. See Cassio wipe his beard with".
At this moment, instead of wanting evidence right away, he instantly wants revenge and that feeling of revenge stays with Othello for the rest of the play. This feeling of revenge is born from a dent in Othello's pride. The idea that Othello has only been married to Desdemona for a short period of time and he has not been able to keep her satisfied for even that long, makes Othello think that he will lose his reputation. He therefore sets out to exact revenge on the person who might have made him the gossip of Venice, and undermined his position as general of the Venetian Army.
Iago does not just use the handkerchief to convince Othello of Desdemona's unfaithfulness. Iago proves to be very good at manipulating people and how they feel. At the beginning of the play Iago successfully gets Roderigo to wake Brabantio and tell him of the relationship between Othello and Desdemona.
