chirl vs undulate

chirl

verb
  • To emit a low sound; to warble. 

noun
  • A kind of musical warble. 

undulate

verb
  • To appear wavelike. 

  • To cause to resemble a wave 

  • To cause to move in a wavelike motion. 

  • To move in wavelike motions. 

adj
  • Changing the pitch and volume of one's voice. 

  • Wavy in appearance or form. 

  • sinuous, winding up and down. 

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