croak vs mutter

croak and mutter both are nouns.

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

As verbs, croak and mutter are synonyms defined as:

Other synonyms of croak include gnarl, grumble, murmur.

croak (noun)	mutter (noun)
a harsh hoarse utterance (as of a frog)	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

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