A low, indistinct utterance under the breath

• A subdued complaint or grumble

压低声音、含糊不清的话语

• 低声的抱怨或嘟囔

To speak in a low, indistinct voice

• To complain under one's breath

低声含糊地说话

• 小声地在心里不满地嘀咕

To make a low, rumbling sound

发出低沉的隆隆声