I really like the screamer idea, not that it would get implemented ;). In order for the experiment to be accurate, we don't need to simulate impact on the human psyche, we just need to bring down the number of psychopaths to a realistic level. Possible solution would be tying the zombie detection range to humanity value - if you have low morality, zombies are more likely to spot you. This would be a solution for "kill on sight" players, and possibly macaroni rambo spawners (if they intend to play a survival game later on, not just CoD at Elektro).