Keep an eye on it
What it can look like. A general, vet-reviewed example — signs vary and this is not a diagnosis. When in doubt, ask your vet. 
Diarrhea / loose stool in dogs
Clinical name: Colitis / loose stool
Soft or loose stools, sometimes more often than usual.
Where it shows upnone
Typical patternN/A.
Linked allergy typesFood allergy
Food vs environmentalGI signs lean strongly toward food.
What you can do
Track consistency; blood, or signs lasting more than a day or two, warrant a vet.
Don't confuse it with
Other causes a vet will want to rule out: infection, parasites, IBD.
This is educational information, not a diagnosis or treatment plan. Always see your veterinarian about your dog's health.
Related signs
VomitingKeep an eye on it
Intermittent vomiting, sometimes after meals.
More frequent stoolsTrack it
Going more than three times a day, sometimes with urgency.
Gas & gut noiseTrack it
Excess gas and audible gut gurgling.
Dull coat despite eating wellKeep an eye on it
A dull, poor coat or weight despite a normal appetite.