mumbling to himself
自言自语
以上为机器翻译结果，长、整句建议使用 人工翻译 。
I could hear him mumbling to himself.
我听到他在喃喃自语。
《牛津词典》
No wonder our bus driver is mumbling to himself.
难怪我们的公车司机一直喃喃自语。
youdao
He was giving a speech, yet he was mumbling away to himself.
他在发言，可却是在喃喃自语。
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