In Darkness level in original mode, make sure you fight the Tower in the sand. When you get to the fourth level, save the man that is going be pulled down by a zombie. After you do, you will look back up and in front of you will be a small square metal gate. Shoot it open and inside will be either Rotten Meat item or other items. Rotten Meat makes all of the zombies heads big. so it is easy to get a head shot.