But for a satisfaction of my thought, No further harm. (III.iii.99-100)
Did Michael Cassio, when you wooed my lady, know of your love? (III.iii.95-96)
My noble lord- (III.iii.93)
What dost thou say, Iago? (III.iii.94)
He did, from first to last. Why do you ask? (III.iii.97-98)
Excellent Wretch! Prediction catch my soul but I do love thee! And when I love thee not Chaos is come again (III.iii.90-92)
I have not deserved this! (IV.i.233)
My lord, this would not be believed in Venice, though I swear I saw't. 'Tis very much. Make her amends, she weeps. (IV.1.234-236)
Now he denies it faintly, and laughs it out. (IV.i.110)
Look how he laughs already! (IV.i.107)
Alas, poor caitiff! (Iv.i.106)
Alas, poor rogue,I think indeed she loves me. (IV.i.109)
Ply Desdemona well, and you are sure on't. Now if this suit lay in Bianca's power, how quickly should you speed! (IV.i.103-105)
I never knew woman love man so. (IV.i.108)
This scene shows the external conflict of Person vs. Person. This is because although secretly, Iago plants the idea of Cassio being an obstacle in the love of Othello and Desdemona into Othello's head. This propels the plot by setting up for the future event of Othello and Desdemona arguing because of Cassio, and this is because Othello will then get agitated by the name "Cassio" and think that he was more than just a messenger in Desdemona and Othello's love life.
The conflict was a person vs. person external conflict between Desdemona and Othello. Othello, thinking that Desdemona had cheated on him with Cassio, got extremely agitated and slapped her in front of Iago and Lodovico. This propels the plot because it tarnishes Othello's reputation that he worked so hard for. This propels the plot because as Othello's reputation is ruined, his life slowly gets more hectic.
In this scene, Iago tempts Cassio to laugh and talk about Bianca, but Othello listens in and thinks that they are talking about Desdemona. This results in a conflict of a one-sided person vs person. This is because Othello is angry and is thinking of ways to kill Cassio, but Cassio does not know that he is in danger, or that he did anything wrong. This scene is important to the plot because it further ruins Othello's trust of Desdemona.