Sick as a horse

a popular simile,—curious, because a horse never vomits.
Horses are said to be extremely sick at their stomachs, from being unable to relieve themselves by vomiting. Bracken, indeed, in his Farriery, gives an instance of that evacuation being procured, but by a means which he says would make the Devil vomit. Such as may have occasion to administer an emetic either to the animal or the fiend, may consult his book for the recipe.