You will shoot at specially-scaled targets which are mounted at a range of 2.5m (8 feet) away. They are sized to simulate targets appearing at various ranges.
There are (up to) 4 stages: 100m, 75m, 50m, and 25m.
For every zombie NOT KILLED on a stage, you face TWO zombies on the next stage. (The commotion and noise attracts more zombies.)
You win if at any time you have killed all zombies facing you. What do you win? Attention on the Internet!
You don't ADD 2, you FACE 2.