flagellum vs riding crop

flagellum

noun
  • A whip 

  • In protists, a long, whiplike membrane-enclosed organelle used for locomotion or feeding. 

  • In bacteria, a long, whiplike proteinaceous appendage, used for locomotion. 

riding crop

noun
  • A horsewhip, short whip used to goad a mount. 

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