Briefly I thought of a crowd of rats beating zombies around as if they
   were worthless.  Since they can't squeak the way a rat does, they just
   moan "braaaains" all day and mess the community up.
   But zombies are badass and don't care in the slightest if they're
   beaten around.  It doesn't help anyone heal.  It's badass to not care
   if you're hurt, it's a cool trait that's held.