Just had a strange run in with a MCed zombie: Der soldier standing right in front of it was trying to stun it with the vanilla stun rod, 10 times in a row (round and round again), but when MCing the zombie afterwards, it still had no stun bar (the blue over red bar). Can zombies simply not be stunned, of what exactly causes this high amount of resilience against the stun rod? Even Mutons or Mechtoid red suits aren't that resilient.