mutter

  1. noun
    a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
  2. noun
    a complaint uttered in a low and indistinct tone
  3. verb
    talk indistinctly; usually in a low voice
  4. verb
    make complaining remarks or noises under one``s breath; "she grumbles when she feels overworked"