While killing zombies once in a while if you kill a special zombie you get what is called a power play, It's when you kill a zombie and a yellow glowing thing appears. there are 5, one says x2 which means double points there is an ammo box which means max ammo, a skull which means ins-ta kill which means they die if you shank them on any round or shoot with one bullet. another one is a hammer which means all the barriers around get rebuild automatically.