Ok, I'll make an example then
As I said before, taken out of context "Piove a catinelle" is an acceptable translation for "It's raining cats and dogs".
Now, let's broaden things a bit. Take this passage, for instance:
"Pioveva a catinelle e non si vedeva in giro un solo animale".
You can tell that in this case it just doesn't make sense to translate the sentence with "It was raining cats and dogs and there wasn't a single animal about". If you do, you're creating a pun that is not there in the Italian original. You'll have to go for something more straightforward, like "It was bucketing down and there wasn't a single animal about".