to sing without opening your mouth: She hummed to herself as she walked to school. 她在上学的路上边走边哼曲子。 to suddenly express strong feelings of anger, disapproval, or disagreement, either by speaking or in a sound that you make: "And you call that a first-class service?" snorted one indignant customer. “你就把那叫一流服务? ”一位愤怒的顾客气哼哼地问道。