In Act 4 Scene 1, What is notable about the use of dashes between lines 19 and 22?

Note the contrast between Othello's language as he falls into a trance, and Othello's language in any previous part of the play, including Act III. He speaks in single, disconnected words‹"handkerchief‹confession‹handkerchief," or "Noses, ears, and lips"‹that completely belie his ability to speak coherently and elegantly, as Othello has shown, especially in Act I with Brabantio. The lack of connection in his language parallels his descent into emotional and logical chaos; as he becomes more upset, without a true cause, he falls farther and farther from himself, and the order which typically rules him. Again, the theme of order vs. chaos comes into play.

So your quote goes like this,

By heaven, I would most gladly have forgot it.

Thou saidst—Oh, it comes o'er my memory,

As doth the raven o'er the infectious house,

Boding to all—he had my handkerchief.

Note the emphasis and pause indicated through the dashes. Othello can't seem to put his torturous thoughts of Desdemona's alleged deceit and his new label as a cuckold into perspective.