Iago is a master of persuasion and employs all three of Aristotle’s “modes of persuasion” throughout the play to bend characters to his will. Iago uses pathos (the mode of persuasion that appeals to people’s emotions) to convince Othello that his wife Desdemona is having an affair with Cassio.
While Iago first tries to persuade Othello of Desdemona’s alleged infidelity through reasoning—for example, by using past evidence of her being deceptive to others—Othello fails to be fully convinced. Instead he becomes frustrated with Iago and demands he show him the “ocular proof” or “make me to see’t”. Iago, knowing it would be impossible to bring Othello actual “ocular proof,” instead uses his language to create a powerful visual image that plays on Othello’s emotions:
It is impossible you should see this,
Were they as prime as goats, as hot as monkeys,
As salt as wolves in pride, and fools as gross
Here, Iago paints Desdemona’s infidelity in animalistic terms designed to invoke Othello’s primal instincts. He goes on to describe Cassio dreaming about Desdemona in his sleep, kissing and sighing. By alluding to the physical act of infidelity itself in vivid terms, Iago forces Othello to picture the scene and invokes his impassioned jealousy. After this passage Othello replies “O monstrous! Monstrous!”, signaling his mental shift as he starts to become convinced that his wife has been unfaithful.
Iago’s use of animal imagery proves particularly effective, with the lewd comparison of Desdemona and Cassio to impassioned goats and monkeys designed to present their alleged passion in graphic terms that infect Othello’s imagination. Indeed, when Othello is later fully in the grips of his jealousy and starting to descend into madness, he nonsensically exclaims, "Goats and monkeys!", confirming that this provocative image has been embedded into his mind.
Iago’s appeal to Othello’s primal instincts in this scene is also apparent with Othello declaring, “I’ll tear her all to pieces,” after Iago’s speech, with this violent response showing Othello’s shift from reason to emotion. The description of tearing Desdemona "to pieces" also invokes animalistic imagery, with Othello presenting himself as a predator descending on its prey. Such an emphasis on animals, creatures of instinct over logic, reinforces the effectiveness of the use of pathos in this scene, with Othello also becoming governed by his emotions.