Shakespeare employs dramatic irony right off the bat. In this conversation between Cassio, Desdemona, and Emilia we see meanings the characters would never even think of reading:
Desdemona: Be thou assured, good Cassio, I will do
All my abilities in thy behalf.
As readers see this, they are reminded of Iago's suggestion to Othello about Desdemona and Cassio having an inappropriate relationship. Here, she means she will do whatever she can to help him win back his relationship to Othello, but readers could interpret that she loves him so much she will do anything for him if they think the way Iago would want them to think.
In Emilia's words, she envokes her husband Iago's concern for the situation:
Good madam, do: I warrant it grieves my husband
As if the cause were his.
Of course Iago "grieves" over this situation, he is desperately trying to put Cassio and Desdemona in a bad position hoping that he will arise a best friend to Othello and therefore get Cassio's job. It is further ironic that she notices her husband's pursuit of the problem "as if the cause were his" because he is the cause!
Right away, Desdemona calls Iago "honest" further developing that dramatic irony in the first five lines of the scene.
Next, in thanks Cassio calls Desdemona "Bounteous woman". Here Shakespeare envokes connotation/denotation. We know the denotative meaning of bounteous is generous. However, we could take the connotative meaning to be a compliment to her womanly bounty. Once again, this is a meaning that Iago would hope we look for as we read into the text and look for the relationship he suggests exists between the two. These double meanings create help feed our disgust for Iago as readers.
Shakespeare uses personification in Cassio's words:
That policy may either last so long,
Or feed upon such nice and waterish diet,
Or breed itself so out of circumstances,
That I being absent and my place supplied,
My general will forget my love and service.
The peronification taking place here builds Cassio's devotion to Othello as he fears his political relationship with the general is dying. It further develops our understanding that Cassio is indeed loyal to Othello as we learn that Othello is beginning to mistrust him.
When Desdemona begins to speak with Othello about Cassio's request, she states:
I have been talking with a suitor here
This word could be taken as a pun. Othello might read the word (which literally means a petitioner) figuratively... as if he is a petitioner of Desdemona, trying to court her.
As she continues her pursuit she uses a simile:
'Tis as I should entreat you wear your gloves,
Or feed on nourishing dishes, or keep you warm,
Or sue to you to do a peculiar profit
To your own person. Nay, when I have a suit—
Wherein I mean to touch your love indeed,(90)
It shall be full of poise and difficult weight,
And fearful to be granted.
Desdemona's plea to have Othello listen to her on behalf of Cassio is important to her. She is comparing her request to simple things she might ask Othello. She is expressing that this is a serious concern and she would not jeapordize her relationship to have him here it. We see Othello deny the request to even hear the suit and realize how much he is believing Iago by how he treats Desdemona. Yet he is still not telling her what he thinks. The great impact here is tenion building and readers do not know who will explode first.