Just tested, and I have to say, there are a lot of things wrong with this mod.
1. The chest cavity is just not necessary, face it, it sucks, it looks good in a screen shot, but when you try it in game, it fails. the Lungs and heart overlap each other when they move, and it looks like he has just eaten baby back ribs, judging by whatever that is below lungs and crap.
2. Are the animations really needed? It makes it look fake when you get a bunch of people doing it because it's perfectly synchronized. And I don't want to be T-baged the whole time when I use this mod. I don't know what people think when they say Headhumpers, but it's not really what a headcrab is, it's a parasite, not something that rapes your head. Barney calls them headhumpers, it's a funny name, that doesn't mean that's what they are and what you should interpret them as when you make this mod.
3. There is a way to get rid of chest cavity, you just teleport. (F7, get fetched)
And there really isn't a point to this other than to goof off, it's like FFC or any hat mod. That isn't exactly a bad thing, but i'm pointing it out :3