sick as a dog

I've got a cold. It sucks. Probably a result of a lack of sleep, damn you long weekend in Surfers and car accident. Anyway, enough whinging, and onto something which has been bugging me for a while - I never figured out where the expression "as sick as a dog" came from. One explanation I found was that it came from the fact that dogs tend to eat just about anything they find, and hence often get sick. Another reasoning for it, which wasn't quite as simple, is this:

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).

At various times cats, rats and horses have been also dragged in to the expression, though an odd thing is that horses can’t vomit; one nineteenth-century writer did suggest that this version was used “when a person is exceedingly sick without vomiting”. The strangest member of the set was used by Jonathan Swift in 1731: “Poor Miss, she’s sick as a Cushion, she wants nothing but stuffing” (stop laughing at the back).

The modern sick as a parrot recorded from the 1970s — at one time much overused by British sportsmen as the opposite of over the moon — refers to a state of deep mental depression rather than physical illness; this perhaps comes from instances of parrots contracting psittacosis and passing it to their human owners.

I don't know about you, but the first one works for me fine... Hmm don't think I'll be able to do any catching up on sleep tonight, but I should probably at least try to minimise the amount I fall behind by...