"random factoid. the phrase "raining cats and dogs is from colonial times when household pets would climb up into the thatched roofs of old houses. when it rained very hard the straw would get slippery and the animals would slide out and fall to the ground. HAHA!"
To clarify, medieval thatched roof houses were small. Animals would often climb on top of the roof for heat, because of the fire/stove running inside the house would warm up the roof.
When it began raining, the roof would get wet and fragile. Without the animals on top of it, the roof itself would have held, but the added weight of the animals caused the roof to tear and the animals would fall through the roof. Hence "it's raining cats and dogs."