Seriously, Vaders breathing didn’t get explained in movies till 20 years after there was 3 movies of him breathing. So what’s the big deal that Grevious coughs? Anyway, that was explained in the first clone wars cartoon. I checked out the dvd and saw it myself. Mace windu crushes his chest with the force.
I probably wouldn’t mind Grevious’ coughing, if Vader hadn’t had it before. Two villains with the same kind of breathing problems is simply unoriginal.
See, before I saw the movie (or maybe early into my viewing of it), I liked the cough. I thought Grevious was gonna be Maul on life support with robot legs. Kind of a beta-Vader that didn’t work as well yet. I would have kinda liked that. But, no.