Basically, this is any child character explaining to his teacher why he hasn't done his homework.
And grass-eating doesn’t usually lead to throwing up -- less than 25% of dogs that eat grass vomit regularly after grazing.
Other suggested reasons why your dog might be eating grass include improving digestion, treating intestinal worms, or fulfilling some unmet nutritional need, including the need for fiber.
Additionally, a number of common house and garden plants are toxic, which could lead to problems if your dog munches on them along with the lawn.
To make sure the plants in and around the area where your dog is eating grass aren’t dangerous, check the ASPCA’s Animal Poison Control Center web site, which maintains a list of toxic and non-toxic plants.