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Mammals have specialized blood vessels in their palms and other hairless skin surfaces—ears, nose, cheeks and soles of the feet—that are designed to dissipate heat. (These radiator-like structures—venous plexuses and arteriovenous anastomoses—were described as early as 1858 in Gray’s Anatomy.) By redirecting blood away from the capillaries and into these blood vessels, the body can shed heat quickly.

Heller and Grahn theorize that more blood, and thus, oxygen, is available to the muscles when the body doesn’t have to route extra blood to the radiators for cooling.