chirl vs stammer

chirl

verb
  • To emit a low sound; to warble. 

noun
  • A kind of musical warble. 

stammer

verb
  • To keep repeating a particular sound involuntarily during speech. 

  • To utter with a stammer, or with timid hesitancy. 

noun
  • A speech defect whereby someone speaks with a stammer 

  • The involuntary repetition of a sound in speech. 

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