OurigamiRoubout is correct I'd just like to add some more details.
The scene:
This was specifically added in the "last minute" to explain the caughcough in the movies because the Clone Wars Grievous did not have the caughcough in previous episodes. As said in the audio commentary on Volume II DVD (my best attempt at transcript):
Genndy Tartakovsky:
We're in this time crunch (...) and he says that George says that Grievous has a caughcough and can you guys maybe put it in and explain how he got the caughcough, because ours obviously does not have the caughcough (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 caughcough. (...)