Legend has it that there was once a water monster called Yu (yù 蜮). It had norns, a shell, wings and three legs, but no eyes. There was a catapult in its mouth. If Yu heard the steps of a man, it would shoot sand from its mouth at him. If even the mans’s shadow was hit, the man would fall ill.

This idiom indicates vilifying people by insinuation.

传说江淮间出产一种很特别的甲虫，名叫蜮，又有人称做射工、射影、短狐、水狐。这种虫常常伤害人，形状很是奇怪，背上长着硬壳，头上有角，身上长有翅膀，可以飞到上空，在人的头上施行袭击。它没有眼睛，但耳朵听觉特别灵敏，口中有一横物，形状像弩，只要听到人声便知道人的所在方向和距离，然后用口中所含的沙当作矢，向人射击。被蜮射中的人，会染上一种毒质而生疮;就算人的身体能够射避，而影子被蜮射中，也会生病。

含沙射影【翻 译】to make oblique charges.