chew vs mumbling

chew and mumbling both are nouns.

Word	Noun	Adjective	Verb	Adverb
chew	Yes	No	Yes	No
mumbling	Yes	No	No	No

As nouns, mumbling is a hyponym of chew; that is, mumbling is a word with a more specific, narrower meaning than chew:

chew: biting and grinding food in your mouth so it becomes soft enough to swallow
mumbling: ineffectual chewing (as if without teeth)

Other hyponyms of chew include chomping, gumming, rumination.

chew (noun)	mumbling (noun)
biting and grinding food in your mouth so it becomes soft enough to swallow	ineffectual chewing (as if without teeth)
a wad of something chewable as tobacco	indistinct enunciation

chew (verb)	mumbling (verb)
chew (food); to bite and grind with the teeth