mutter vs croak

mutter and croak both are nouns.

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

As verbs, mutter and croak are synonyms defined as:

Other synonyms of mutter include gnarl, grumble, murmur.

mutter (noun)	croak (noun)
a complaint uttered in a low and indistinct tone	a harsh hoarse utterance (as of a frog)
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

mutter (verb)	croak (verb)
make complaining remarks or noises under one's breath	pass from physical life and lose all bodily attributes and functions necessary to sustain life
talk indistinctly; usually in a low voice	make complaining remarks or noises under one's breath
	utter a hoarse sound, like a raven