Word Detective tells us something interesting that we hadn't considered. When we think of "sick as a dog" we need to keep in mind what that meant back in 18th century Europe.
Back then, to "be sick" didn't mean to feel unwell, it referred to tummy troubles. Specifically the kind where you vomit.
|photo: Creative Commons 3.0|
And since dogs historically have a bit of a reputation in this department (well, they will eat almost anything, we've heard...!) the reference kinda makes sense.
As the phrase moved through the centuries, sometimes other animals were dragged into the mix, including cats, rats and even horses. (Which is interesting, actually, since we learned horses cannot vomit!)
Though the weirdest version goes - paws down - to the one Jonathan Swift used in his book Polite Conversations, written in 1738: "Poor Miss, she's sick as a cushion, she wants nothing but stuffing."
Um...huh? Or, as one of the peeps our mom works with says, "Whatevs!"
sources: All Experts, Word Detective and Worldwide Words