"神不知鬼不觉"用英语怎么说？

“神不知鬼不觉”，中文俗语，字面意思是“unknown to god or ghost”，形容事情做得很秘密，别人一点也不知道。可以翻译为“without anybody being aware of，not noticed by anyone”等。

例句：

他们设法神不知鬼不觉地离开了海岸。

They managed to get away from the coast undetected.

怎么会有人神不知、鬼不觉地潜入皇宫呢？

How could anyone break into the palace undetected?