OurigamiRoubout is correct I'd just like to add some more details.

The scene: https://www.youtube.com/watch?v=j1UPccudqmU

This was specifically added in the "last minute" to explain the caugh in the movies because the Clone Wars Grievous did not have the caugh 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 caugh and can you guys maybe put it in and explain how
> he got the caugh, because ours obviously does not have the caugh (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 caugh. (...)