To make a sound with a low, rumbling noise.
To speak softly and incoherently, or with imperfect articulations.
To utter words, especially complaints or angry expressions, indistinctly or with a low voice and lips partly closed; to say under one's breath.
A repressed or obscure utterance; an instance of muttering.
Peas.
To make a squeaking sound.
The squeaking sound made by a guinea pig or other cavy.