Anal glands are scent glands located on either side of the anus i think at 8 and 4 ish. The normal bowel movement of a dog expresses them naturally. Most dogs never need them expressed and some chronically have problems. Even to the point of and anal gland abscess. that is when the anal gland doesnt get expressed and builds and builds until it breaks open. This doesnt happen that often. If you notice your dog scooting nine times out of ten it is trying to express its own glands. It does not mean it has worms. or if you notice he or she licking at there rear end a lot. there are a few other things that might cause and odor from that end, like UTI (urinary tract infection) which can sometime have an ordor, or in some spayed females they can get incontience issues and they leak urine which can smell bad, kinda musty odor. But if you have smelled an anal gland expression believe me you wont forget it. Hope that helped some.