His last rebellion, his final influence over the situation -- knowing nothing. And its ironic because he was the source of all knowledge and information that sparked all the events, and now that everything is done, he is still. There is no more movement, even if they would like there to be some. In this way he is really like Shakespeare, having the power to cause and inhibit action through knowledge -- the greed of which is Othello's fatal flaw.

The dirty satisfaction of knowing is what tears everything down. The desire of knowing the full truth once it has been handed a little to you -- curiosity kills the cat. In this way Iago is the fruit of TEMPTATION!