What transpires in the brwl among Cassio, Roderigo and Iago?

Act V, scene i:

Summary:

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 Ludovico also stumble upon the scene, having no idea what has happened. Roderigo is still alive, so Iago feigns a quarrel, and finishes him off.