I have been confused by Grima crying, there was an article in the Dominion Post (Newspaper of Middle Earth) where Brad Douriff said he played Grima in that scene as suddenly realising his actions would result in the destruction of most of the surviving humans and lead to the victory of Saruman, a last vestage of his humanity and sorrow for what he had just done and what would happen.
Then later I read / heard on the EE that this was joy at a job well done and Grima was in awe of the massive army.
IT seems as if there are several stories out there, each contradicting the other, possibly to inspire debate or just to screw with the minds of people like us!
