1.when pigs fly不可能发生的事 2.put the cart before the horse 本末倒置 3.sweating like a pig汗如雨下 4.let the cat out of the bag 泄密 5.black sheep害群之马 6.dog days三伏天 7.every dog has its day凡人也有得意时 8.rain cats and dogs 倾盆大雨