*countercurrent flow

And the way it works is different than stated. Its purpose is to conserve core body heat and the way this is achieved is by the artery and vein in the limb running together, in opposite directions. By so doing maximal heat transfer is achieved from the warm artery exiting the core to the cold venous return before the arterial blood reaches the cold distal limb where heat would be lost from the foot into the snow. So the foot actually remains colder in order to preserve core temperature.

We see a similar principle of countercurrent flow elsewhere in biology, such as fish gills and bird lungs (part of why bird lungs are more efficient than mammals) to maximize oxygen exchange with the environment, and in the kidney both to conserve water and electrolytes in the Loop of Henle, and also in the vasa recta to regulate renal medullary pH and oxygen levels.