The line of zombies needed kill non-human opponents in an area that is tough to access during a living dead match in Halo. Usually most zombies in a lame train act as cannon-fodder dying within a second of attacking the hiding Spartans but every now and then one is lucky enough to kill a human and turn them into a fellow zombie.
Zombie Player 1: Hey guys, these 4 noobs are camping at the end of that dead end tunnel and we need to infect them.
Zombie Player 2: Good call. Everyone form a lame train at the other end of the tunnel. We'll rush them once we're all there. They have shotguns and magnums so chances are most of us will die but one of us should be able to get them with our plasma sword.