He's got THREE SHOTS! TWO SHOTS! ONE SHOT!

It's toward the end of the film, when Amber and Pat are trying to escape. Two of the last skinheads come into the room to kill them; Pat is down in a bunker underneath the floorboards, and Amber hides under the couch cushions; she hears the two skinheads discuss how much ammunition they have left in their gun.

One of the guys goes down into the bunker to get Pat, and Amber slowly crawls out of the couch and kills the other guy by sneaking up behind him with a box knife. She then uses his body (as well as the body of another skinhead and the body of her friend) to distract the other skinhead by dropping the bodies down into the bunker, causing him to shoot his rifle and waste his ammunition. That's why she's yelling "He's go three shots! Two shots! One shot!" because she's letting Pat know when his gun is out.

I had no idea that was her from the trailers. I probably wouldn't have known if I hadn't seen her name in the cast.

It was a great scene.