Endothermy, colloquially referred to as warm-bloodedness, was the physiological ability of some creatures to control their body temperatures through metabolic means, notably by burning food within themselves. To keep a being's body temperature high even in cold weather, that process required that being to use more food. In hot weather, the body of an endothermic being had ways of cooling itself off through perspiration—a process which, at least in Humans, produced a distinct smell. The opposite of endothermy was ectothermy. All mammals, including Humans and Krytollak, and most avians were warm-blooded lifeforms. While endothermic reptiles existed, they were not overly common.