Zombies are incredibly stupid. If players are in a group, they will focus on just one of the two players, even if th eone they focused on gets downed, they will just stand around him while the other players could kill them without any concern. A really cool idea with this plugin, is they can sense gunshots and explosions and run towards them. With that being said, they stop and "analyze" everytime this happens. They're just too easy to kill and don't really pose any threat to anyone.