Explain what Iago does to Cassio and Roderigo. Infer why he takes the action he does against Roderigo.

Iago has Roderigo poised and ready to pounce on Cassio, and kill him; if either of them is killed, it is to Iago's benefit, although he would like to have both of them disposed of, so that his devices might not be discovered. Roderigo and Cassio fight, and both are injured; Othello hears the scuffle, is pleased, and then leaves to finish off Desdemona. Iago enters, pretending that he knows nothing of the scuffle; Gratiano and Lodovico also stumble upon the scene, having no idea what has happened. Roderigo is still alive, so Iago feigns a quarrel, and finishes him off. Bianca comes by, and sees Cassio wounded; Iago makes some remark to implicate her; Cassio is carried away, and Roderigo is already dead. Emilia also comes in, and pins more blame on Bianca; she has done nothing, but Iago has some quick work to do if he is to exonerate himself in this mess. Iago kills Roderigo because he knows to much and Iago has no use for him anymore.