Rudolph's nose isn't red just so that it can light the night sky for Santa -- it's packed with red blood cells so that it doesn't freeze in the frigid temperatures, according to a scientific take on a classic Christmas tale published in the British Medical Journal.
Those red blood cells in reindeers' noses also help to keep their brains at the right temperature, said researchers from Erasmus University Rotterdam, University of Amsterdam, and University of Tromso.
For the study, researchers compared the blood vessels of five human noses with those of two reindeer noses. They found that "the nasal microcirculation of reindeer is richly vascularised, with a vascular density 25 percent higher than that in humans," they wrote.
"These results highlight the intrinsic physiological properties of Rudolph's legendary luminous red nose, which help to protect it from freezing during sleigh rides and to regulate the temperature of the reindeer’s brain, factors essential for flying reindeer pulling Santa Claus’s sleigh under extreme temperatures," they wrote.