Centaur vs serpent

Centaur

noun
  • One of a race of monsters having a head, torso, and arms of a man, and the body and legs of a horse. Often depicted as rowdy drunkards, with Chiron being a notable exception. 

  • A skillful horseman or horsewoman. 

  • A U.S. upper stage, with a restartable liquid-propellant engine, used with an Atlas or Titan booster to launch satellites and probes. 

  • An icy planetoid that orbits the Sun between Jupiter and Neptune 

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 Centaur and serpent occurred in a corpus of books? (source: Google Ngram Viewer )