As is well-known, it never rains cats and dogs. Therefore, people keep wondering where the odd phrase came from. It surfaced in print in the middle of the 17th century, and the hypotheses of its origin are numerous. Some of them pretend to explain only the reference to cats and have no value by definition. Others are pure fancy. Such as the idea that torrential rains used to carry along with them the refuse of the streets, including many dead animals. Somebody who has never read Scandinavian myths suggested that in northern mythology cats are said to be influenced by the coming storm and that the weather god Odin’s animals were hounds. But Old Norse cats had nothing to do with rain, while Odin was not a weather god and never owned dogs.
Yet a sensible explanation of the idiom seems to exist. The phrase “it rained cats and dogs and pitchforks” has been recorded. Also, in 1592 a reliable author wrote: “Instead of thunderbolts shooteth nothing but dogboltes and catboltes.” The words ‘dogbolts’ and ‘catbolts’, denoting ‘iron bars’, are still current in dialects. The original idea was that a downpour of sharp objects fell to the ground.