Discuss what Iago promises him and he says to do if it doesn't happen. Argue another characteristic this scene reveals about Iago.

Iago is a master manipulator. He not only calms Rederigo's rage but gets Roderigo to do more of his bidding. Iago tells Roderigo that if he (Roderigo) isn't having sex with Desdemona then Roderigo has every motive to stab him (Iago) in the back. I think Roderigo only hears the sex with Desdemona part and again shows what a sap he is to Iago's manipulations.