Some animals are big and dangerous and, when hungry, may realise that humans contain a pretty decent amount of meat. I've never hiked in such areas, but they do exist.
Photo from Wikipedia, CC-BY-SA 3.0
When on tour in Svalbard (and presumably in other polar bear territory as well), one is required to carry a rifle in order to protect oneself when attacked by a bear.
But what about during the night? Must someone stay awake all night to keep guard in case a polar bear comes for human meat?