Definition: to speak too quietly and not clearly enough for someone to understand you Level: B2
他咕哝着说这是在浪费时间。
He ___mumbled something about it being a waste of time.
她太紧张了，演讲时开始含糊不清地说话。
She was so nervous that she started ___mumbling during her speech.
别咕哝了，请大声点说！
Stop ___mumbling and speak up, please!
