Actually those zombies never talks in game, they just screaming gibberish.
They're "killing each other" like zoo monkeys.
Damn.. i thought the indian Airlines were better...
I always feel sorry for the commons because even when idle, they show what I believe a shred of remaining humanity which is why they look depress and move almost more human than zombie. Just when they're startled, the infection works into there remaining humanity to make them feral.