When not in use, it's retracted by a woodpecker, & it may wrap around under the skull, beneath the skin
Similarly the nostrils of woodpeckers are protected from being flooded with 
... As tools, bills are not used just for eating food, but also for catching it, prying up 
bark ... wrap all the way around the bird's skull under the skin when it is retracted
... [DOC] [TLE] Bird of the Month: The Acorn Woodpecker - The Toast [PAR] Jul 30, 2014 ... Large white-billed woodpecker, demonstrating its strong beak ...