Yes, the word grumble is a noun, a word for the sound that the bear was making.
The word grumbling is the main verb, the action of the bear.
In your sentence, the word 'grumbling' is the main verb('was' is the auxiliary verb).
The bearded bear is known for his humble grumble, which is sometimes used to great effect on creatures of the fairer sex.
The correct 'bare' to use in the sentence ''toonice to bear'' is actually 'bear,' which means to tolerate or endure.
When I visited the zoo, I saw a Grizzly Bear.
The word is "bear" (to have, incorporate, or exhibit).
1. I see a BEAR in the meadows.
There is no need to capitalise the word 'koala' in a sentence. Nor do you use the word 'bear', as koalas are not bears.
boobaly bear
Bear is an animal. Bear skins are used as rugs and covers; their flesh is eaten.
davy's pet bear
The bear used his bare feet to walk .
The cart was unable to bear the heavy load.