Emilia finds Desdemona's handkerchief which she drops when talking to Othello. Emilia then gives it to Iago who only just showed up. Iago is nothing more than overjoyed.
Othello isn't putting up with Iago's incessant belligerence towards his wife and the crude remarks that Iago can't prove. Othello then takes Iago by the throat and threatens him.
If there is no proof thou shall perish.
Cassio gives Bianca Desdemona's handkerchief for some reason as he doesn't explain . Bianca thinks there is more to herself and accepts the gift. She tries to guess the meaning behind the handkerchief, but to no avail. Cassio says that her guesses are meaningless.