bleat vs mutter

bleat

verb
  • Of a person, to complain. 

  • Of a sheep or goat, to make its characteristic cry; of a human, to mimic this sound. 

noun
  • The characteristic cry of a sheep or a goat. 

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 bleat and mutter occurred in a corpus of books? (source: Google Ngram Viewer )