喃喃低语

例句：

1. 1.He mumbled something under his breath as he walked past the window.
   他悄悄地在走路经过窗户时嘟囔着什么。
2. 2.She mumbled an apology to her boss after she made a mistake.
   她在犯错后向老板低声道歉。
3. 3.The old man mumbled about his life experiences in the park.
   老人在公园里低声谈论着他的生活经历。