It's raining cats and dogs. @ 英語學習筆記

It's raining cats and dogs.
A great idiom and one that paints a very colorful picture. However... if there is one thing that show up a competent speaker of English as someone who hasn't really fully grasped the language, it's an over-reliance on idioms. In everyday life, we just don't tend to use them, and so coming from a non-native speaker they seem forced and unnatural. Far more appropriate is :
'It's raining heavily.'

Rain can be described as 'heavy' or 'light' depending on its intensity.
Several other things can also be described in this way:

heavy light	sleeper drinker smoker
－－－－－－－－－－－－－－
heavy light	traffic rain

e.g. You'll never wake him up -- he's a heavy sleeper.
Sorry I'm late, the traffic was very heavy.

    這句話是一句很好的成語，也帶給人豐富的想像空間。但如果直譯的話，會變成正下著貓與狗。
    但實際上，這句話代表的意思是「現在正下著傾盆大雨」。
    然而，如果我們認為會使用這句片語，就代表語言能力很好的話，那就是對語言有誤解，並過度信任片語帶給每個人的意義了。在日常生活當中，我們盡量不去用這些片語，而且從非以英語為母語的人士口人講出這些，會令人感覺很勉強又不自然。

    下雨可以用 "heavy" (大) 或 "light" (小) 來形容，取決於雨下的強度而定。有許多事物也可以用 heavy 及 light 來形容其程度，如下：