BONUS: If it's "raining cats and dogs," it's raining very hard outside. No one is sure where this phrase comes from.
額外福利：如果外面在“下貓和狗”（raining cats and dogs），說(shuō)明雨下得很大。沒(méi)有人確切知道這句習(xí)語(yǔ)的來(lái)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)."
研究者稱(chēng)，據(jù)歷史記載，此短語(yǔ)是個(gè)押韻俗語(yǔ)，來(lái)形容“青蛙在起風(fēng)暴時(shí)被卷到天上，下雨時(shí)又隨雨水摔到地面”。

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."
另外一個(gè)出處可能是最早出現(xiàn)于1592年的一句話（收錄在《牛津英語(yǔ)詞典》中）：“這下的哪里是雷雨，分明是在下鐵釘。”。

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是鐵螺釘，通常用來(lái)固定房門(mén)或院門(mén)，而cat bolts則通常被用來(lái)將幾塊木頭固定在一起。換句話說(shuō)，這兩個(gè)詞將暴風(fēng)雨比作從天上掉下來(lái)的重重的金屬釘。在某些情況下，省略bolt也許是因?yàn)橥嫘Γ苍S是因?yàn)檎f(shuō)起來(lái)順口，所以這個(gè)習(xí)語(yǔ)的本意在今天并說(shuō)不通。

英文來(lái)源：businessinsider
譯者：實(shí)習(xí)生孫美真
審校&編輯：丹妮