Wyatt Earp speaking of Doc Holliday. Doc Holliday's father, Henry B. Holliday was a trained pharmacist who served in several wars, including the Cherokee Indian War, the Mexican War, and as a Major in the Confederate Army.
Dogs frequently eat grass to ease stomach discomfort. If your dog's stomach is empty, the grass may cause your dog's stomach to produce more digestive enzymes, and this can result in vomiting bile. Unless your grass is treated with fertilizer or pesticides, it's generally safe to allow your dog to continue eating it, as it can help ease her stomach problems.
Grass has emetic properties. By instinct, cats and even dogs seem to know this. So very often when they eat something that gives them an upset stomach (nausea) or an indigestion, they eat grass and very soon the offending food in the stomach is vomited. With cats it's usually a hairball that's stuck somewhere in the gastrointestinal tract. The grass blades surround the hairballs and cause the cat to vomit them out.