I would ask - What type of food are you feeding?
Dogs do this often as you have read in other answers, which generally are correct about upset stomachs or dog just needs to chew a bit.
Look at the ingredients in your food and make sure they are using high quality specific meat proteins. Not too much in grains if any at all, fresh fruits and vegetables.
I use Orijen and my dogs and cats love it:
www.championpetfoods.com