This monk is meditating in freezing cold, and one Tibetan Buddhist practice, g tummo, is known to measurably raise body heat. In the early 1980s researcher Herbert Benson measured monks warming their fingers and toes by several degrees. A 2013 study found forceful vase breathing generated the heat, while visualization helped sustain it. It's my favorite example of how the body can do far more than we train it to.