Answer:
Cassio expresses to Desdemona in the "Othello" of Shakespeare's Act III and asks her to act as a mediator on his behalf with Othello. She decides to speak of Cassio with her husband repeatedly till their quarrel got patched up.
At that moment, Othello and Iago enter. Cassio feels embarrassed for previous night’s antics, embraces Desdemona and leaves. Desdemona's body language with Cassio gives Iago the chance to poison Othello’s mind about Desdemona’s infidelity.
Iago’s words remind him of Brabantio’s words. In between Iago gets hold of Desdemona’s handkerchief from his wife Emilia. Still not willing to give into his negative thoughts Othello has dinner but the thoughts racing in his mind don’t put him to ease. He asks for proof and Iago tells a dream story about Cassio.
He also states him that with a handkerchief he noticed Cassio dry his eyes. Othello acknowledges this hankie when he sees it as the one he offered Desdemona. Thus, Cassio’s conversation with Desdemona and observing her body language with him gave Iago the golden opportunity to give a structure to the next step of his malicious plan.
