These Alaskan frogs freeze almost completely at the start of winter, with two-thirds of their body water turning into ice. To all intents and purposes, they seem dead; their heart stops beating, and their blood flow stops. However, once winter starts to thaw so do they and they hop back to life.

DJ L, L M, H V, et al. Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance. J Exp Biol. 2014;217(Pt 12):2193-2200. doi:10.1242/JEB.101931