Winter arrives in the Arctic, the temperature drops, and the Wood Frog responds accordingly. That is, it freezes. First it drifts into a deep sleep, then its heart stops, its breathing stops, and most of the water in its body turns to ice. The Wood Frog becomes, for all intents and purposes, a frog-shaped Popsicle. But when spring arrives some months later, an interesting thing happens: the frog thaws, and its hearts starts to pump again, its breathing resumes, and the animal is soon hopping, croaking, mating -- enjoying all the amphibian pleasures life has to offer.
What's the Wood Frog's secret? Well, slow cooling is important. If the animal's temperature were to drop too quickly, it wouldn't have time to secrete substances like glucose that protect its internal organs from dehydration while frozen. Slow cooling also allows the water inside the frog time to shift position. The more water that collects in the hollow cavities within the abdomen, for example, the more room there is for the water to expand as it freezes. If too much water remains in the organs, however, blood vessels will rupture as the temperature drops, and the animal will never wake from its slumber.
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