mumble vs mussitate

mumble

verb
  • To speak unintelligibly or inaudibly; to fail to articulate. 

  • To chew something gently with closed lips. 

noun
  • A quiet or unintelligible vocalization; a low tone of voice. 

mussitate

verb
  • To say (words, etc.) indistinctly; to mutter. 

  • To talk indistinctly; to mutter. 

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