Describe how Iago sets up the plot to make Othello believe Cassio is having an affair with Desdemona.

Iago has his wife take the scarf that Desdemona has dropped. He starts a rumor that Cassio has been seen wiping his brow with it. Othello asks Desdemona for the scarf and, of course, Desdemona can't produce. Also Desdemona wants to heal the rift between Cassio and Othello. Othello takes this as further suspicion which drives his paranoia.Bianca, Cassio's lover/prostitute, shows up with the scarf as well.