Raining cats and dogs

This goes back many hundreds of years to the Dark Ages, when people believed in all sorts of ghosts, goblins and witches and even thought that animals, like cats and dogs, had magical powers. The cat was thought to ride in the storms were often pictured as black cats. Dogs and wolves were symbols of winds and the Norse storm god Odin was frequently shown surrounded by dogs and wolves. So when a particularly violent rainstorm came along, people would say it was raining cats and dogs– with the cats symbolizing the rain and the dogs representing the wind and storm.