Antifreeze
According to Lauren Livo, a herpetologist and Ph.D. candidate at University of Colorado in Boulder, glucose and glycogen are used as ice-growth controlling substances in wood frogs and chorus frogs. Both wood frogs and chorus frogs hibernate fairly close to the surface.
These ice-growth controlling substances may drop the freezing point somewhat, but more importantly, they cause the ice crystals that do form to be granular (a granular form is less likely to damage tissues) instead of long, sharp, and knife-like (which is much more likely to damage tissues).