Quote 22
IAGO
If I can fasten but one cup upon him
With that which he hath drunk tonight already,
He'll be as full of quarrel and offense
As my young mistress' dog. (2.3.49-52)
Iago schemes to get Cassio drunk because he knows Cassio, who is kind of a mean drunk, will end up getting into a fight. Why? Because he wants Cassio (a soldier) to get in trouble with Othello (Cassio's boss/general) so that Desdemona will try to intervene on Cassio's behalf, which will make Othello jealous and suspicious. If this sounds overly elaborate and unrealistic to you, you're not alone. Literary critics often point out that much of Iago's plotting is, well, pretty implausible.
IAGO
Ha! I like not that.
OTHELLO
What dost thou say?
IAGO
Nothing, my lord; or if—I know not what.
OTHELLO
Was not that Cassio parted from my wife?
IAGO
Cassio, my lord! No, sure, I cannot think it
That he would steal away so guiltylike,
Seeing you coming.
OTHELLO
I do believe 'twas he. (3.3.37-44)
Gosh. Iago is an evil genius, don't you think? After watching Desdemona and Cassio chit-chat from afar, Iago suggests that something naughty is going on between Cassio and Othello's wife. He never comes right out and says, "Hey Othello, look at your wife flirt with Cassio," but he implies there's something tawdry happening and then acts all innocent when Othello presses the point.
Quote 24
IAGO
Demand me nothing. What you know, you know.
From this time forth I never will speak word. (5.2.355-356)
This is the last time Iago speaks in the play. After Othello demands to know why Iago set out to destroy him, Iago remains silent. But why? One would think that Iago would want to gloat but he refuses to explain his actions, leaving Othello and the audience pretty clueless about Iago's motives.