Everything above 27,000 feet is known as the death zone. Mount Everest is over 29,000 feet high, so the last 2,000 feet are up in the death zone. Once you enter the death zone, your body starts to die. At that altitude, even wearing an oxygen mask, you brain starts to function differently and becomes confused very easily. At this altitude, every movement is exhausting, and when people die on Everest, there is little anyone can do to get their bodies down off of the mountain. There are somewhere around 200 bodies that are still on Everest because there is no way to get them down. One of the most famous is Green Boots (in the picture below). His real name was Tsewang Paljor, who died on the mountain in 1996. He is seen by every climber that gets to the summit using the North East Ridge.