Stacked Zombies are a more rare variety of zombie that consists of at least three zombies stacked on top of each other.
Known to have much greater health then normal zombies, it is best to avoid engagement with Stacked Zombies until you have some decent weapons. They are capable of surviving a shot from the Military Sniper, although they won't have much health remaining afterwards.
This zombie is real, although authenticity regarding other wiki posts would bring this into question. Please post videos and pictures in order to back this up further.