mumble vs utter

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. 

utter

verb
  • To reveal or express (an idea, thought, desire, etc.) with speech. 

  • To produce (speech or other sounds) with one's voice. 

  • To put (currency) into circulation. 

  • To commit the crime of uttering (knowingly presenting forged documentation). 

  • To produce (a noise) (of an inanimate object). 

adj
  • Absolute, unconditional, total, complete. 

  • Outer; furthest out, most remote. 

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