for most of this movie I was thinking: "Why is that robot coughing? thats so dumb" and then later: "oh, ok"

In the clone wars cartoons, Greivous encounters Mace Windu and gets his torso crushed while he kidnaps Palpatine, hence the coughing fits.

HEY, thanks for clearing that up. I gotta rent those clone wars dvds. I heard they're swell.