It appears that Desdemona and Cassio are having an affair. In reality, they are not.
It appears that Desdemona has Cassio in her heart when she pleads for his reinstatement as lieutenant. In reality, she is just doing him a favor.
It appears that Cassio slips away from Desdemona when he sees Othello coming. In reality, Cassio was just giving Desdemona space to talk with Othello about being reinstated as lieutenant.
It appears that Desdemona has given her most cherished handkerchief to Cassio. In reality, Iago planted the handerkerchief on Cassio.
When Iago and Cassio are talking, it appears that Cassio is laughing and talking about his affair with Desdemona. In reality, he is talking about Bianca, his mistress.
It appears that Iago is Othello's friend. In reality, Iago is Othello's worst enemy.