Accuracy is king in Zombie Hunter Inc, so to facilitate this you can only aim to the left or right. It's kind of fitting seeing as how the zombies crawl in horizontally, so don't think of it as that big of a handicap. Strafe across the screen, move, shoot, move again, shoot again. That's the key! Hitting zombies in the head is also the key, because everybody knows that's the only way to re-kill them.