These animals aren't dead. They are putting on a remarkable performance. Birds enter this trance like state quite readily. Frogs who appear to die and turn on their backs, but it's just a bluff. The hognose snake lolls its tongue to fake death throws and gives off the stench of decay. It was the opossum that gave death-feigning its name. As it plays possum, anal secretions make it smell like a rotten corpse. This behaviour is easily triggered by hypnosis techniques and the animals often wake up together. They play dead because most predators won't touch carrion.