nothing (III. iii. 75). Happy with Othello's answer, Desdemona leaves the garden and Iago, alone once again with Othello, continues his evil machinations. He asks if Cassio knew about Othello's love for Desdemona from the beginning of their courtship. Othello says yes and adds that Cassio even served as a matchmaker for the two and 'went between [them] very oft'.
Iago shows deep concern and subtly hints that Cassio's ulterior motive had been all along to engage in an affair with Desdemona. Iago plays upon Othello's insecurities, reminding him that Cassio is younger and more handsome and is a white Venetian citizen. It does not take long before Othello is convinced of Desdemona's betrayal. He chooses the words of Iago over his trust in his wife, and declares 'my relief must be to loathe her.' (III. iii. 268).
Desdemona enters with Emilia to call Othello for supper. He tries to hide his inner turmoil but Desdemona can tell that he is troubled. He complains that he has a headache. She pulls out a handkerchief embroidered with strawberries and lovingly puts it to his head, but he pushes it away and it falls to the ground. Othello insists she not bother picking it up, and he tells her that he is ready for supper. For some time Iago has asked Emilia to steal Desdemona's handkerchief and now, alone in the garden, she has the opportunity.
Hiding it in her pocket, Emilia wonders what Iago's intentions are for the handkerchief. Iago enters and Emilia proudly shows him the handkerchief. He calls her a 'good wench' and she asks him for what purpose will he use it. He refuses to tell her and she leaves on his command. Once alone, Iago reveals what Emilia desired to know: I will in Cassio's lodging lose this napkin/And let him find it' (III.
iii. 321-2). Othello returns from his short supper and he is distraught to say the least: 'Farewell, tranquil mind' (III. iii. 350). Desdemona's treachery consumes his thoughts and he lashes out at Iago, demanding immediate proof of her betrayal.
Iago makes up a story that placed him outside Desdemona's chamber a short time before, and he tells Othello that he heard Desdemona professing her love to Cassio. Othello rages 'I'll tear her to pieces' and Iago adds that he has seen Cassio with Desdemona's handkerchief -- the first gift Othello ever gave her. Othello cries for 'blood! blood! blood!' (III. iii. 451) and kneels before his confidant Iago, taking a vow of revenge: Now, by yond marble heaven, In the due reverence of a sacred vow.