What are examples of dramatic irony in Othello?

Dramaticis when a playwright creates a
situation where the audience is aware of something that the characters in the play are not.
Throughout the entire play, the audience is aware that Iago is manipulating the other characters
without them knowing. An excellent example of dramatic irony takes place in Act Four, Scene 1.
Iago attempts to convincethat Cassio has been sleeping with Desdemona by telling Othello to hide
and watch as Cassio jokes about his affair with her. Iago tells Othello,

"Do but encave yourself, and mark the fleers, the gibes, and
notable scorns that dwell in every region of his face. For I will make him tell the tale anew
where, how, how oft, how long ago, and when he hath, and is again to cope your wife. I say, but
mark his gesture" (Shakespeare, 4.1.71-77).

In
reality, Iago plans to discuss Cassio's relations with Bianca because Cassio cannot help but
laugh when he talks about her. Iago explains his plan to the audience by saying,

"As he [Cassio] shall smile, Othello shall go mad. And his
unbookish jealousy must construe poor Cassios smiles, gestures, and light behavior quite in the
wrong" (Shakespeare, 4.1.90-93).

While Iago speaks
to Cassio about Bianca, Othello believes that Cassio is laughing about his affair with
Desdemona. The audience is aware that Othello is being manipulated as he hides and watches
Iago's conversation with Cassio. Cassio is also unaware that Othello is watching as Iago plots
against him. After Cassio leaves the scene, Othello immediately asks Iago how he should go about
murdering Cassio. Iago also convinces Othello that Desdemona gave her handkerchief to Cassio.
Again, the audience is aware that Iago has acquired the handkerchief from Emilia and has placed
it in Cassio's room.

Throughout the entire scene, Othello believes Iago's
lies and accepts the story of Desdemona's infidelity under false pretenses. The dramatic irony
creates suspense as the audience witnesses Iago's evil plans take root and influence the other
characters to act upon his lies.