How does Iago trick Otello into misunderstanding Cassio’s laughter?

In Verdi’s Otello, Iago tricks Otello into misinterpreting Cassio’s laughter by manipulating the context of their conversation while Otello watches from a hidden location.

In Act III, Iago instructs Otello to hide and observe him as he brings Cassio into the room. Iago then encourages Cassio to talk about his amorous adventures with his mistress, Bianca. As the two men discuss these affairs, they begin to laugh. Because Otello is concealed and cannot hear the specific subject of their conversation, he assumes the laughter is directed at Desdemona and his own supposed cuckoldry, which fuels his rage. Iago further solidifies this deception by showing Otello a handkerchief that he had previously stolen from Desdemona, leading Otello to believe it is proof of her infidelity.12