Break the ice
打破僵局，缓解紧张气氛
Hit the nail on the head
一针见血，说得非常准确
Let the cat out of the bag
泄露秘密
Piece of cake
小菜一碟，非常容易的事
Under the weather
身体不适，感觉不舒服
Once in a blue moon
千载难逢，极为罕见