Okay but we're arguing over sound, and I think zombies had super hearing someone would've said it. We have a scene dedicated to explaining zombie senses, and in it the characters do not conclude they have enhanced hearing.
Again this is more a knock on the humans, nobody ever calls them sneaky, they just happen to be in every corner because without people making sounds they just stay around a spot after the person died. It's not stealth mastery, they are just abundantly everywhere
This is not a 9-C feat. I can break glass like that if I ram myself through it. Also, not making sounds and then surprising someone because you jumped through a window is not stealth mastery.
Yes, generally it's far easier to tear an object after you bit off a big chunk of it. So I disagree with this being 9-C for anything besides the bite.
Also no it does not, the further you are from an explosion the weaker it gets, and they clearly got very injured from it.