mamroczący Englisch:

She's muttering something.

I have no doubt that many of them are imprisoned in mental hospitals, or they are among the muttering homeless who refuse integration into society 2. God knows what's happening in that madman's mind,' she muttered.

He's mumbling something.

why are you mumbling?

... he had heard people mumbling and grumbling--" I have...

He was still mumbling something about hospitals at the end of the party when he slipped on a piece of ice and broke his left leg.