catch someone red-handed
If someone is caught red-handed, they are found doing something wrong or illegal.
如果有人手还红的时候被抓到,表示他正在做违法的事情时被发现。最初,是用来指一个人正在杀人,手还粘满鲜血时就被发现了。所以,手才是红色的。后来他的意义越来越广泛,用来指人正在做任何错事或违法的事情是时被发现。所以,不管你是头番茄酱、巧克力还是大白菜,颜色都不变了,都是红色时被抓!
伊人独酌 tried to cheat on the exam, but her teacher walked in and caught her red-handed. (伊人想考试作弊,但被老师抓了个现行!)
, when I was in primary school, I looked for the solution in the book, in fact, the teacher didn't find me, but I shaked and the book was shaken down, and the teacher found me
When students cheat in the exams they feel much afraid. Even though the teacher doesn't find them cheating they themselves get the attention of the teacher by their unnatural behavoir.