ferret vs least weasel

ferret

noun
  • The black-footed ferret, Mustela nigripes. 

  • A diligent searcher. 

  • An often domesticated mammal (Mustela putorius furo) rather like a weasel, descended from the polecat and often trained to hunt burrowing animals. 

verb
  • To uncover and bring to light by searching; usually to ferret out. 

  • To hunt game with ferrets. 

least weasel

noun
  • The common weasel, little weasel, or simply weasel (Mustela nivalis), the smallest member of the weasel genus Mustela, native to Eurasia, North America, and North Africa. 

How often have the words ferret and least weasel occurred in a corpus of books? (source: Google Ngram Viewer )