During Chapter Two, in front of the gate that you need to open are two zombies sleeping on the ground. Do not use the crank for the gate yet, as it will wake them up. Lure another zombie to them, and shoot him in the leg so that he falls to the ground. When all three are close together, drop a match to burn them and get the "Drop It Like It's Hot" achievement. If you fail to kill all three zombies, load your last auto save to try it again. Just make sure the third zombie lands on top of the two sleeping zombies. If you are out of matches, you can find some in the buildings of this area.