The metabolic slowdown reduced her oxygen demand.

The physiological triage that her body performed protected her core organs at the expense of her peripheral tissues.

The heating pads reversed the process, degree by degree, until her body’s own heat-generating capacity could take over.

What the science does not fully explain — what probably cannot be fully explained — is exactly how close to the edge Jean Hilliard’s core came on that December night.

How low did her core temperature fall?