moan vs mutter

moan

verb
  • To say in a moan, or with a moaning voice. 

  • To complain; to grumble. 

  • To grieve. 

  • To make a moan or similar sound. 

noun
  • a low, mournful cry of pain, sorrow or pleasure 

mutter

verb
  • To utter words, especially complaints or angry expressions, indistinctly or with a low voice and lips partly closed; to say under one's breath. 

  • To speak softly and incoherently, or with imperfect articulations. 

  • To make a sound with a low, rumbling noise. 

noun
  • A repressed or obscure utterance; an instance of muttering. 

  • Peas. 

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