Grass moves in the blowing wind
A small change or disturbance, or the sign of either of these
Neutral
你留在这里继续监视，一有风吹草动，就打电话通知我 | Nǐ liú zài zhèlǐ jìxù jiānshì, yī yǒu fēngchuīcǎodòng, jiù dǎ diànhuà tōngzhī wǒ
You stay here and keep an eye on things. If anything changes, call me immediately and let me know
[Source]
现在，政策上的任何风吹草动都可能对地产价格产生重大影响 | Xiànzài, zhèngcè shàng de rènhé fēngchuīcǎodòng dōu kěnéng duì dìchǎn jiàgé chǎnshēng zhòngdà yǐngxiǎng
Right now, any slight change in government policy could have an enormous impact on housing prices
[Source]
None
None
Most sources that I referenced had varying accounts of this story
《敦煌变文集》(Dūn Huáng Biàn Wén Jí), a compilation of literature written in the Táng Dynasty (唐, 618 - 907)
During the Spring and Autumn Period (春秋时代 | chūn qiú shí dài | 770 - 476 BC), there was state named 楚国 (Chǔ Guó), and one of its kings was named 楚平王 (Chǔ Píng Wáng). 楚平王 was rather fond of women, and eventually, he became so bold as to move on his own daughter-in-law.
This behavior disgusted the high-ranking minister 伍奢 (Wǔ Shē), who then vocally opposed the monarch's actions. Enraged, 楚平 responded by having the minister and his eldest son executed.
Word of this reached the ears of 伍子胥 (Wǔ Zǐ Xū), the executed minister's second son, and he knew that he had to flee for his life. His best chance for safety was in the kingdom of 吴国 (Wú Guó), and so it was to there that he began the arduous journey.
One night, he arrived at a river's edge and began to search for someone to ferry him across. He found an old fisherman to do the task, but when they arrived at the other side, the fisherman told him that he was going to find something for him to eat, and 伍子胥 grew very frightened. He hid amongst the reeds, barely daring to breathe as he waited for the man to betray him and return with government troops.
When the old fisherman returned, however, he carried nothing with him but a hearty meal. 伍子胥 emerged from the reeds and ate gratefully, then continued on his way to 吴国.
He made it to 吴国 successfully, and once there, he helped the country flourish. Finally, after many years, he helped lead a military campaign against his old state. After they achieved victory, 伍子胥 found the grave of 楚平王, prized it open, and whipped the corpse inside. Then, finally, he felt that he had gotten his revenge.
In the source for this chengyu, the author notes that during 伍子胥's perilous journey, even the slightest rustle of the grass terrified him into thinking that he was going to be captured by pursuing government troops. It is from this that the chengyu 风吹草动 originated.