Does Grievous have a mouth and/or vocal cords?

Perhaps the gutsack is designed to maintain a constant pressure. I mean, there is a certain level of air pressure inside your body at all times, which is balanced out by the air pressure around you. When pressure outside drops or increases, your body has to compensate. We have a mechanism inside our ears that keeps our ear drums from exploding out/in when we're on a plane, and the rest is regulated somehow (not sure). In space, however, you're in a vacuum, so perhaps the gutsack keeps a constant pressure on the organs.

 

Matt's got it. They're not exactly under pressure, they're pressurized. Like the inside of a spaceship.

 

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