My dogs always did that. I noticed that it always seemed to be after a huge meal the night before. My vet says it's normal for dogs to do this, they will sometimes eat grass to help settle their stomach. Could be a stressful event from the day before and digestion wasn't proper. I don't mind cleaning it up off the floor, but when it's on the carpeting it has to be done right or it will stain. You could try adding enzymes to the diet too.