This is arguably the best known of all English idioms.
Raining cats and dogs. If you look carefully, you'll see them on the cover of the English Idioms Explained ebook series.
Britain is famous for its wet weather and can you believe that when it rains really heavily, cats and dogs actually fall out of the sky? That's how the idiom came about.
Only joking - it is after all, just an idiom!
If like me, you find the sound of rain relaxing, then you'll enjoy this peaceful video. Of course, it's best to be inside in the warm and dry when it's raining cats and dogs outside.