神不知，鬼不觉(Shén bù zhī, guǐ bù jué)doing things secretly

Explanation

“神不知，鬼不觉”的字面意思是说神不知道，鬼也没察觉到。比喻做事非常秘密，没人知道。
The literal meaning of “神不知,鬼不觉” is that gods don’t know and ghosts don’t detect. It metaphorically describe doing things secretly.
Words:

走廊zǒulánɡ:corrido;
摄像头shèxiànɡ tóu:camera;
记录jìlù:record;
教室jiàoshì:classroom.

Sentences

1、Tā běnlái yǐwéi zìjǐ zuò de shén bù zhī guǐ bù jué, qīshí, zǒuláng lǐ de shèxiàngtóu jìlù xià le yíqiè.
他本来以为自己做得神不知鬼不觉，其实，走廊里的摄像头记录下了一切。
He thought no one knew what he had done. In fact, the camera in the corridor recorded all.

2、Nà nánhái shén bù zhī guǐ bù jué de liūchū le jiàoshì.
那男孩神不知鬼不觉地溜出了教室。
That boy slipped out of the classroom without being noticed.