It's Raining Cats and Dogs

Your Native English Teacher's idiom of the week:
Well, this one is suitable for the crazy rain I have been trudging through this week.

It's raining cats and dogs.

This idiom means that it is raining very heavily.

The man was running quickly through the street, dodging people's umbrellas. It was raining cats and dogs.

I was interested where this idiom came from so I did a little research. The most common explanation says that in olden times, homes had thatched roofs in which domestic animals such as cats and dogs would like to hide. In heavy rain, the animals would either be washed out of the thatch, or rapidly abandon it for better shelter, so it would seem to be raining cats and dogs.

I also found a mythological explanation.

It seems that cats were at one time thought to have influence over storms, especially by sailors, and that dogs were symbols of storms, often accompanying images and descriptions of the Norse storm god Odin. So when some particularly violent tempest appeared, people suggested it was caused by cats (bringing the rain) and dogs (the wind).

Who knows where it really came from, but it is a good one to keep in your pocket.