Ferret

Ferrets are small mammals mentioned once in How to Be a Pirate in the How to Train Your Dragon Book series.

Description
Ferrets (Mustela putorius furo) are weasel-like creatures that are considered a domesticated sub-species of the European Polecat. Ferrets have been used to hunt small game, especially rabbits, for at least two millennia.

Ferrets are small carnivores with very flexible, long bodies and short legs, suitable for moving through burrows. Their ancestors, the European polecat, can be found in the warmer areas of Scandinavia, but cannot tolerate Arctic or sub-Arctic climates.

Function
In the Book series, ferrets are mentioned as a metaphor. However, in real life, ferrets are predominantly pets in present day, though they are also used in medical research. Historically ferrets were used for hunting small game.

How to Be a Pirate
A ferret is mentioned when describing Gobber's wild beard:

"OKAY YOU DRIPPY LOT!" yelled Gobber, a six-and-a-half-foot hairy muscle-bound lunatic, with a beard like a ferret having a fit and biceps the side of your head."

- Book 2