Raining cats and dogs

We say it's raining cats and dogs when there is a heavy downpour. It simply means a heavy rain. The saying presents an interesting image of animals falling from the sky, that doesn't seem to have much to do with torrential rain, and experts aren't certain about its origin. The most likely and least appealing theory is that rain storms in 17th century England would carry the bodies of dead animals through the dirty city streets inspiring people to say "it's raining cats and dogs"