The heart, driven by electrical impulses generated by specialized cells, can maintain a rhythm at temperatures far below the normal range — but the rhythm slows, and the strength of each contraction diminishes, and the volume of blood circulated with each beat falls.

The brain, which requires a constant supply of glucose and oxygen to maintain consciousness and then to maintain any function at all, reduces its activity as its temperature falls.

At some point in those six hours, Jean Hilliard’s outward appearance became indistinguishable from that of a corpse.

Her face, pressed into the snow, was frozen.

Her extremities were frozen.

Her skin had taken on the gray, waxy appearance of flesh from which blood has withdrawn, because the blood had indeed withdrawn from the skin — shunted inward to protect the core in a last-ditch physiological effort at survival.

Her heartbeat had slowed to a rate so low that it was undetectable without specialized equipment.