BONUS: If it's "raining cats and dogs," it's raining very hard outside. No one is sure where this phrase comes from.
额外福利：如果外面在“下猫和狗”（raining cats and dogs），说明雨下得很大。没有人确切知道这句习语的来源。
The researchers for the study said this phrase is "an instance of rhyming slang after frogs were whipped into the air during a storm and came back down again with the rain (as testified to in historical accounts)."
研究者称，据历史记载，此短语是个押韵俗语，来形容“青蛙在起风暴时被卷到天上，下雨时又随雨水摔到地面”。
Another possible origin comes from a 1592 sentence (documented by the Oxford English Dictionary) that reads: "Instead of thunderboltes shooteth nothing but dogboltes or catboltes."
另外一个出处可能是最早出现于1592年的一句话（收录在《牛津英语词典》中）：“这下的哪里是雷雨，分明是在下铁钉。”。
The "dog bolts" were iron bolts to secure a door or a gate, while "cat bolts" were used to fasten together pieces of wood. In other words, they likened a heavy rainstorm to heavy metal bolts falling out of the sky. At some point, "bolt" was dropped either as a joke or to make it easier to say, causing the phrase to make no sense today.
Dog bolts是铁螺钉，通常用来固定房门或院门，而cat bolts则通常被用来将几块木头固定在一起。换句话说，这两个词将暴风雨比作从天上掉下来的重重的金属钉。在某些情况下，省略bolt也许是因为玩笑，也许是因为说起来顺口，所以这个习语的本意在今天并说不通。
英文来源：businessinsider
译者：实习生孙美真
