Mucus in the stool with no other signs cannot be readily linked to any particular disorder and may not infer any illness. Mucus is produced by the colon in order to help facilate the evacuation of the stool (pooping made easier). Occasionally more mucus than 'usual' can be made. It can also be made secondarily to any colonic inflammation which can include intestinal parasites, bacteria, swallowed foreign objects, and unusual foods. If the clinical signs are more than once - you may want to contact your veterinarian. If other clinical signs such as diarrhea, blood in the stool, lethargy, etc... are seen then I would go immediately to your veterinarian.
Good luck.
