Dogs eat anything, and I mean ANYTHING. But that leads to some troublesome consequences. Dogs get sick when they eat something unusual, like chocolate for instance - which can even cause death.
But where did the phrase, "Sick as a dog" come from?
The English language is always changing, so to pinpoint the original use is impossible. But one can infer that because dogs frequently get sick from consuming items that don't digest well, that the same goes for us humans. You're as sick as a dog when you just don't feel right.
Some interesting analysis by World Wide Words
: "There are several expressions of the form sick as a ..., that date from the eighteenth and nineteenth centuries. Sick as a dog is actually the oldest of them, recorded from 1705
; it is probably no more than an attempt to give force to a strongly worded statement of physical unhappiness. It was attached to a dog, I would guess, because dogs often seem to have been linked to things considered unpleasant or undesirable; down the years they have had an incredibly bad press, linguistically speaking (think of dog tired, dog in the manger, dog’s breakfast, go to the dogs, dog Latin — big dictionaries have long entries about all the ways that dog has been used in a negative sense
The phrase itself has also been muddled. Some now say, "I'm sicker than a dog." That's actually what I thought was the original phrase, but later learned that was not the case.
I'd put this phrase in the same sort of folklore as Every Dog Has Its Day, Drunk as a skunk, or any other silly animal personification.
I always enjoy posting funny responses to nodes:
The Debutante says re sick as a dog: (Apparently, dogs won't eat hedgehog innards.)
gnarl says re sick as a dog: "This writeup deserves mention of one of the greatest webster 1913 definitions ever."
Dog"sick` (?), a.
"Sick as a dog sometimes is very sick."
The Debutante says "And oh, a vomiting dog is not a pleasant experience. But did you know that horses can't vomit?"