Barefoot in subzero temparatures

Yikes:

Dmitry built up astonishing endurance, and could hunt barefoot in winter, sometimes returning to the hut after several days, having slept in the open in 40 degrees of frost, a young elk across his shoulders.

Src: http://www.smithsonianmag.com/history/for-40-years-this-russian-family-was-cut-off-from-all-human-contact-unaware-of-world-war-ii-7354256/?no-ist