In Act 4 Scene 1, What is the misunderstanding that occurs in the conversation between Desdemona, Lodovico and Iago. What must Othello think?

The contrived conversation between Iago and Cassio that Othello ‘overhears’ is even more successful than Iago had hoped due to the intervention of Bianca. She possesses the valuable handkerchief that is a token of Desdemona and Othello’s love. She is nought but a whore and it makes Desdemona’s relationship with Cassio even more sordid. Othello at this stage is unable to view things dispassionately and so far as he is concerned this is the hard evidence he sought in order to prove his wife’s infidelity. Iago now speaks openly and insultingly regarding Desdemona and even suggests to Othello how he might kill her.

Lodovico’s arrival carrying a message from the Duke provides an independent witness for Iago. He sees the violence between Othello and his wife and Iago suggests that Othello is going mad. Iago has now set the wheels in motion. He does not require taking any further action and just has to wait on his plans unfolding.

Originally it had been Iago’s plan to possess Desdemona as part of his humiliation of Othello. He has to let go of this notion as Othello is determined to murder his wife.