Later in the scene, in order to undermine Othello’s confidence in Cassio, Iago beings to ask questions about him without revealing the thoughts behind them or why he wants to know, “Did Michael Cassio, when you wooed my lady, / Know of your love…But for a satisfaction of my thought; / No further harm.” (Lines 95-96/97-98) Iago then repeats Othello’s words as questions, this mysterious behaviour frustrates Othello, he is concerned Iago is harbouring “some monster” in his thoughts and demands to know what he is thinking. When Iago refuses to tell him he claims it is for his own good, “It were not for your quiet nor your good…To let you know my thoughts.” (Lines 152-154), These techniques anger Othello further, yet makes Iago seem loyal and concerned for his lord.
By holding back his thoughts and repeating his faith in Cassio’s honesty, Iago also appears loyal to whom he maintains is his friend, “For Michael Cassio, /I dare be sworn I think that he is honest.” (Line 125-126) This gives Othello no reason to believe Iago is lying about Cassio, as he has no motive to accuse him of seducing Desdemona. By confirming his loyalty and love for Othello, “My lord, you know I love you.” (Line 117), Iago encourages him to trust his suspicions and evidence of adultery.
Another persuasive technique employed by Iago is reverse psychology. At one point in the scene he advises Othello against exactly what he wants him to do, overreact and become obsessed with suspicion “I am to pray you not to strain my speech/To grosser issues, nor to larger reach/Than to suspicion.” (Lines 217-219) Othello claims he is not affected by Iago’s doubts however he begins to wonder how people can betray their true natures “I do not think but Desdemona’s honest…And yet, how nature erring from itself-“ (Lines 224/226)
Iago often uses play-acting to further persuade Othello that Desdemona has been unfaithful to him. By appearing shocked and offended at Othello’s accusation he is lying, “O grace! O heaven defend me! /Are you a man? Have you a soul or sense?…I’ll love no friend, sith love breed such offence.” (Lines 371-378) and seemingly regretful of telling his lord his suspicions “I do repent me that I put it to you.” (Line 390) Iago seems honest and devoted to Othello, giving Othello little reason to doubt him.
During the scene Othello goes through stages of jealousy, insinuated by Iago, who is the first to mention the word jealousy, “O beware my lord of jealousy; /It is the green-eyed monster which doth mock/The meat it feeds on.” (Lines 164-166) However, Othello replies he is never jealous without proof, which gives Iago the opportunity to present his suspicions of Desdemona’s infidelity, “Look to your wife; observe her well with Cassio; /Wear your eyes thus, not jealous nor secure.” (Lines 196-197) Iago then uses Desdemona’s past to persuade her husband she is dishonest. By hiding her marriage to him and pretending to her father she was afraid of Othello, Desdemona was deceitful, “She did deceive her father, marrying you; /And when she seemed to shake, and fear your looks, /She loved you the most.” (Lines 205-207) This makes Othello even more suspicious of his wife, yet he still believes her to be honest.
All Iago has had to do to Othello is make him doubt Desdemona and his jealousy intensifies until it consumes him. To finally convince Othello that Desdemona committed adultery with Cassio, Iago needs proof and Othello demands circumstantial evidence. Although Othello demands proof that his wife is unfaithful before he will accept it, he seems sure he has lost her before he receives any such evidence, “Haply, for I am black/And have not those soft parts of conversation/That chamberers have; or, for I am declined/Into the vale of years- yet that’s not much-/She’s gone.” (Lines 261-266) he blames his age, skin colour and lack of manners for Desdemona's infidelity.
The only proof Iago can provide is a dream he witnessed Cassio having, in which he kissed Desdemona and placed his leg over hers, however this enough to make up Othello’s mind that his wife has been unfaithful. He has been fooled by Iago and vows to seek revenge, he can think of nothing but murder “O, blood, blood, blood!” (Line 450) and appoints Iago his lieutenant. Othello has been manipulated and his susceptibility is the fatal flaw which will lead him to his downfall.
