AP Photo

A small brown frog squats motionless in a den of green moss. It inhales no breath, has no heartbeat, yet it is not dead. Rock hard and icy to the touch, this speckled North American wood frog is frozen alive at –2?°C, and has been so for the last 24 hours.

Then Jon Costanzo adjusts the temperature of the terrarium, and the air around the frog begins to warm.