The disgusting smell of death of death is the result of certain airborne molecules with evocative names like cadaverine and putrescine. These molecules are not produced by death, however, but by life growing on death. After an animal dies, its cells self destruct and become food for the body's resident bacteria. They chew through the walls of the gut and spread through the body. They release cadaverine and putrescine merely as byproducts of their metabolism. These molecules are not actually dangerous to us. They won't kill us like a whiff of sarin or cyanide. Yet our ancestors evolved a keen sensitivity to these molecules, along with an instinctive response to recoil at the merest whiff. Life's Edge: The Search for What It Means to Be Alive