Wednesday's Random Slang-o-rama: Raining cats and dogs

The phrase raining cats and dogs popped into my mind while I was writing. My first thought was: How old is it? It sounds "old enough." My second thought was: Why cats and dogs? Why not snakes and lizards? Or apples and oranges?

So of course, I had to set aside my draft and go a-searching for answers.
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Christine Ammer's The American Heritage Dictionary of Idioms notes that this phrase means "to rain very heavily." (Yep, I knew that.) It also had this to say about its origins:

The precise allusion... which dates from the mid-1600s, has been lost, but it probably refers to gutters overflowing with debris that included sewage, garbage, and dead animals. Richard Brome used a version of this idiom in his play The City Wit (c. 1652), where a character pretending a knowledge of Latin translates wholly by ear, "Regna bitque/and it shall rain, Dogmata Polla Sophon/dogs and polecats and so forth."

The online Grammarist lists another possible reference and adds details to the "dead animals in the street after a heavy rain" origin:

There are several theories, one being that the phrase raining cats and dogs references the mythologies of the Norse god Odin and English witches. Odin was depicted as traveling in storms with dogs and wolves, cats were well-known familiars of witches.

Another possible source of inspiration ... is the filth of seventeenth century London. Stray animals lived and died untended. When streets became swollen with rain it is likely there were many dead dogs and cats floating in the flooded streets, giving the appearance of having rained cats and dogs. The oldest known use of this term occurred in 1651, in a  collection of poems by Henry Vaughan in which he alludes to a roof that was secure against “dogs and cats rained in shower.”

Not quite ready to return to my draft, I checked the Online Etymological Dictionary, where someone had fun writing up this entry:

...One of the less likely suggestions [for the origin of this phrase] is pets sliding off sod roofs when the sod got too wet during a rainstorm. (Ever see a dog react to a rainstorm by climbing up on an exposed roof?)

Ooops, pardon me, Etymological Dictionary, your rhetorical question is showing... ;-)

And because I was in a procrastinating mood, I delved a little deeper and unearthed this fascinating post from the Library of Congress on the phrase raining cats and dogs. You can't beat the Library of Congress for thoroughness (or great images).

Up with the bumbershoots! Four-footed creatures are falling from the sky in great abundance! 
George Cruikshank [Public domain]