I've been re-watching Star Wars after picking up the BD pack, and one thing that's been bothering me is the smoker's cough that General Grievous displays. Since he's (at least) half cybernetic, there should be no reason for organic maladies to persist. I don't think that he even has lungs, so the cough is completely simulated. Given that, at least in today's world, such a condition would generally be frowned upon, why does he still carry around this trait from his organic life?
He does have lungs and they were injured by Mace Windu in the Clone Wars (Chapter 25)
As he fled, Jedi Master Mace Windu Force crushed the plates covering Grievous's internal organ sac, injuring his lungs and aggravating the General's already irritating wheezing and coughing problems; a result of his organic form not taking well to his cyborg implants. This crippling blow injured Grievous for the rest of his life
OurigamiRoubout is correct I'd just like to add some more details.
This was specifically added in the "last minute" to explain the cough in the movies because the Clone Wars Grievous did not have the cough in previous episodes. As said in the audio commentary on Volume II DVD (my best attempt at transcript):
We're in this time crunch (...) and he says that George says that Grievous has a cough and can you guys maybe put it in and explain how he got the cough, because ours obviously does not have the cough (voice was not yet decided) and I go Howard.. we have a week left or a month left before we deliver. So this sequence right here was all after that. We kinda got together, we talked about it and I go.. OK let's have Mace crush his chest and that's how we'll introduce the cough. (...)