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. Within 30 minutes, the amphibian’s skin noticeably softens, taking on its characteristic sheen. Three hours later, one eye blinks. Then the lungs shudder to life, and the frog’s sides heave. Six hours from the start of warming, one leg twitches, then the other. Finally, as the timer chimes 10 hours, the frog hops once, twice, and burrows out of sight into the moss.
“I’ve been doing this for 25 years now, and still, whenever we freeze the frogs and watch them recover, it seems magical,” says Costanzo, a cryobiologist at Miami University in Ohio. But though it may look like hocus pocus, the frog’s dramatic transformation is cold, hard fact.