This frog freezes solid and wakes up

The Alaskan wood frog spends its winter as a literal rock. It stops breathing, its heart stops beating, and its blood ceases to flow while its internal organs are encased in ice.

Most animals die when they freeze because ice crystals shards pierce cell walls like tiny needles. The wood frog avoids this by flooding its blood with glucose and urea. These chemicals act as a biological antifreeze, lowering the freezing point and keeping the interior of the cells liquid even while the spaces between them turn to ice.

For up to seven months, this frog is clinically dead. It sits under leaf litter, frozen stiff and brittle, waiting for the spring thaw.

When the temperature rises, the frog's entire body thaws simultaneously. Within hours, its heart spontaneously restarts, and it hops away to find a mate as if nothing happened.

This process is so efficient that the frog can survive temperatures as low as zero degrees Fahrenheit without any brain damage or tissue loss. Space agencies are currently studying these frogs to see if humans could ever mimic this suspended animation for long-distance space travel.