They are glands either sid of the anus, scent glands, that coat each poo th dog does, if th poo is solid enough. Bulking up stools with bran helps ensur a firm enough poo for th glands to hopfully empty normally, but sometimes thy ned to b expressed by a vet or groomer if it doesn't normally happen. The dog may hav a strong fishy smll and scoot on it's bottom.