Contrary to popular believe it isn’t that common for your dog to vomit after eating grass. Some researchers believe that dogs use grass as self medication to ease stomach upsets, which is why your dog may eat grass and then be sick.
A dog eating grass to make itself vomit
However, less than 25% of dogs that eat grass vomit afterwards. A lot of the time dogs eat grass because they need more fibre in their diet or if they are bored. Eating grass is considered a natural dog behaviour so it is nothing to worry about.