It Is Raining Cats and Dogs

As the rain falls in sheets of water outside my window, I was reminded of an email that had a lot of sayings we have formed through history.  This one seems appropriate for this day.

Where did the saying, "It's raining cats and dogs come from?"

During the 1500's, houses had thatched roofs-thick straw-piled high, with no wood underneath. It was the only place for animals to get warm, so all the cats and other small animals (mice, bugs) lived in the roof. When it rained it became slippery and sometimes the animals would slip and fall off the roof. Hence the saying, "It's raining cats and dogs."

Now we are all smarter :)  What popular sayings do you know the history behind?