草cǎo木mù皆jiē兵bīng

Literal: grass and trees, all soldiers
Figurative: To be so panic-stricken that one sees enemies everywhere; jumping at shadows out of fear.

Where does 草木皆兵 come from?

At the Battle of the Fei River (383 CE), Fu Jian, ruler of the Former Qin, climbed a city wall after an early setback to observe the enemy Eastern Jin army. Seeing their orderly ranks and gazing at Mount Bagong, he mistook even the grass and trees on the slopes for enemy troops drawn up for battle. That dread foreshadowed his crushing defeat.

Source (出处): 《晋书》

How is 草木皆兵 used? Two examples

听tīng说shuō小xiǎo区qū里lǐ出chū了le小xiǎo偷tōu，她tā吓xià得de草cǎo木mù皆jiē兵bīng，连lián风fēng吹chuī门mén响xiǎng都dōu以yǐ为wéi有yǒu人rén闯chuǎng进jìn来lái。
When she heard there was a thief in the neighborhood, she got so jumpy that even the wind rattling the door made her think someone was breaking in.
疫yì情qíng最zuì严yán重zhòng的de那nà段duàn时shí间jiān，大dà家jiā草cǎo木mù皆jiē兵bīng，有yǒu人rén咳ké嗽sou一yī声shēng整zhěng车chē厢xiāng的de人rén都dōu紧jǐn张zhāng起qǐ来lái。
At the height of the epidemic everyone was so on edge that the moment someone coughed, the whole train car tensed up.

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