what does iago tell othello about meeting between cassio and desdemona? what is othello's response?

Iago seizes on this opportunity to play on Othello's insecurities, and make Cassio's exit seem guilty and incriminating. Othello then speaks to Desdemona, and Desdemona expresses her concern for Cassio; she is persistent in his suit, which Othello is not too pleased about. Othello says he will humor her, and the subject is dropped for a while.

Iago then plays on Othello's insecurities about Desdemona, and gets Othello to believe, through insinuation, that there is something going on between Desdemona and Cassio. Othello seizes on this, and then Iago works at building up his suspicions. Soon, Othello begins to doubt his wife, as Iago lets his insinuations gain the force of an accusation against her. Othello begins to voice his insecurities when it comes to Desdemona, and himself as well. Desdemona enters, and they have a brief conversation; Othello admits that he is troubled, though he will not state the cause.