As he shall smile, Othello shall go mad, and his unbookish jealousy must construe. Poor Cassio's smiles, gestures, and light behaviors quite in the wrong.
By heaven, that should be my handkerchief!
Let the devil and his dam haunt you!..I was a fine fool to take it!...This is some minx's token, and I must take out the work!..
How now, my sweet Bianca? How now? How now?
A most unhappy one. I would do much t' atone them, for the love I bear to Cassio.
What, is he angry?
Fire and brimstone!
Are you wise?
Iago is going to talk to Cassio about Bianca which will make him happy. Othello will see this interaction and will misinterpret the conversation thinking they are talking about Desdemona, further infuriating him.
Beshrew him for't! How come this trick upon him?
Nay, heaven doth know.
I will be hanged if some eternal villain, some busy and insinuating rogue, some cogging, cozening slave, to get some office, have not devised this slander. I will be hanged else.
Bianca confronts Cassio about the handkerchief that he gave to her. Othello sees that it is his handkerchief that he gave to Desdemona, likely thinking that she gave the handkerchief to him.
Unless his abode be lingered here by some accident-wherein none can be so determinate as the removing of Cassio.
How do you mean, removing him?
Why, by making him uncapeable of Othello's place: knocking out his brains.
Desdemona tries to reply to Lodovico about the strained relationship between Cassio and Othello, which sends Othello into a yelling rage. Othello then slaps Desdemona in front of Lodovico. Iago finally plaguing Othello's mind.
All's one. Good faith how foolish are our minds! If I do die before thee, prithee, shroud me in one of those same sheets.
Come, come, you talk!
Iago and Emilia try to comfort Desdemona about how Othello has been treating her. Iago says that some trick must have caused this, but ironically the trick is Iago himself who has flooded Othello's mind with all these scenarios. Emilia has no idea that Iago is the villian.
Rodreigo confronts Iago about how his payments are leading to no results. Iago then says that to get Othello and Desdemona to stay in Cyprus a bit longer, he must kill Cassio so he can't take Othello's place. Iago convinces Roderigo that it is his duty to kill Cassio.
Desdemona talks to Emilia about if she dies, she wants to be wrapped in wedding her bed sheets . Foreshadowing the fact that she is going to die in her bed.