Dogs frequently eat grass, which is a harmless activity. Some dogs seem to act like mini lawnmowers, eating grass at every opportunity. Others dogs eat grass only occasionally, subsequently throwing it up.

"It's a normal part of their diet," says Holly Frisby, DVM, of Doctors Foster & Smith, Inc. in Wisconsin. Wild canine relatives of dogs--wolves and foxes--eat all of an animal when they catch it. They end up, therefore, eating grasses and plants in the intestines of these animals. Domestic dogs, eating prepared dog food, lack this part of their diet and so they eat grass.

Explanations abound, but rationales such as that it neutralizes acid, or that eating grass might make the dog vomit, so dogs eat grass to remove unwanted substances from their stomachs, are at best educated guesses.

Dogs may appear to eat grass, when they are just running the blades through their mouth to gather information. Their sense of smell and taste may act together to detect if other animals have walked through their area or urinated on the grass.