This squirrel's body temperature drops below freezing without turning to ice
Hibernating Arctic ground squirrels let their core body temperature fall as low as -2.9°C, the coldest ever recorded in a mammal, while their blood and tissues stay perfectly liquid. There's no antifreeze involved — they survive through supercooling, a fragile state where fluids stay unfrozen below their normal freezing point as long as nothing disturbs them. They rewarm themselves every couple of weeks, all winter long.