"she grumbles when she feels overworked"
Are you muttering threats at me?
你是在咕咕哝哝地对我说威胁话吗?
He was muttering away to himself.
他不停地喃喃自语。
She muttered away in the dream.
她在梦中咕咕哝哝地抱怨。
She was muttering to herself.
她不停地喃喃自语。
mutter sth to sbShe muttered a few words to us.
她低声地抱怨了我们几句。