Really nice mechanic! I've seen a lot of games where you're trying to control a bunch of sheep or cats or whatever, but this is the first game I've played where getting the hoard out of control is actually the goal. It has the same addictive quality as something like agario, where you're basically growing something as massive as possible. One thing I'd change would probably be the level format, it's kind of disheartening to restart every level at one zombie. I'd love to see an arcade style of this where humans keep spawning, and maybe the more zombies you have the harder they are to convert and the more damage they deal. As is though, this is still a great game.