I Hear:
In Act III, Iago attempts to convince Othello that Desdemona has been unfaithful to him. Iago plants the seed that Desdemona and Cassio are having an affair. Othello believes Iago but needs to have some type of physical evidence. Iago obtains Desdemona's handkerchief, which was a gift to her from Othello and plans to place it in Cassio's room. This will help convince Othello that his wife has been unfaithful and Othello will probably kill both Cassio and Desdemona.
I Notice:
It seems somewhat hard to believe that in the short time they have been on Cypress that Desdemona and Cassio could have had an affair. Likewise, it is somewhat confusing that Othello quickly assumes that his wife is having an affair.