gnarl vs mutter

gnarl and mutter both are nouns.

Word	Noun	Adjective	Verb	Adverb
gnarl	Yes	No	Yes	No
mutter	Yes	No	Yes	No

As verbs, gnarl and mutter are synonyms defined as:

Other synonyms of gnarl include croak, grumble, murmur.

gnarl (noun)	mutter (noun)
something twisted and tight and swollen	a complaint uttered in a low and indistinct tone
	a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

gnarl (verb)	mutter (verb)
make complaining remarks or noises under one's breath	make complaining remarks or noises under one's breath
twist into a state of deformity	talk indistinctly; usually in a low voice