“Why Do Dogs and Cats Eat Grass? (A) They Are Sick and Need to Vomit. (B) They Have a Dietary Deficiency. (C) Studies Point to a Third Option That May May Well Be the Correct Answer to This Often-Asked Client Question”, 2008-12-01 (; backlinks; similar):
[2-page popular summary of et al 2008: a survey of dog owners about plant-eating found that it was common, usually didn’t seem related to illness, occasionally triggered vomiting, younger dogs did it more, and no diet appeared correlated with plant-eating. Similar preliminary results for cats are mentioned.
Hart interprets these results as support for his theory that plant-eating is an evolved behavior intended to help control intestinal parasites, mechanically through fiber going through the intestines but also partially through vomiting.]