nostril vs stool pigeon

nostril

noun
  • Either of the two orifices located on the nose (or on the beak of a bird); used as a passage for air and other gases to travel the nasal passages. 

stool pigeon

noun
  • A pigeon tied to a stool by a piece of twine, used as a decoy to entice free-flying birds to the ground to be shot or trapped. 

  • An informer to the authorities, especially one who gives up criminal associates. 

How often have the words nostril and stool pigeon occurred in a corpus of books? (source: Google Ngram Viewer )