mammal vs serpent

mammal

noun
  • A vertebrate with three bones in the inner ear and one in the jaw. 

  • An animal of the class Mammalia, characterized by being warm-blooded, having hair and producing milk with which to feed its young. 

serpent

noun
  • A snake, especially a large or dangerous one. 

  • An obsolete wind instrument in the brass family, whose shape is suggestive of a snake (Wikipedia article). 

  • A kind of firework with a serpentine motion. 

  • A subtle, treacherous, malicious person. 

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