Definitions for "Mumbling"
Low; indistinct; inarticulate.
indistinct enunciation
speaking low and indistinctly; "a mumbling parson stood beside the dying man"; "muttering crowds of onlookers"
Keywords:  ineffectual, chewing, teeth
ineffectual chewing (as if without teeth)
motion that is not distinct in application. Can be compared with words that lack diction.