Anal glands are two small secretory pouches located just inside the opening of the anus. They’re used in scent marking and to assist in communicating with other dogs. Anal glands usually empty while a dog is doing a poo, or sometimes when he or she is frightened, but sometimes they can become blocked. One theory is that some commercial foods cause dogs to produce smaller poos, and this may result in the glands not having enough pressure exerted on them to empty properly while your dog goes to the toilet. It can also be caused by intestinal worms, or infection. Signs your dog's anal glands could be blocked include dragging, or "scooting" their bottom along the floor, accompanied by much licking of the affected area.