Dogs get tapeworms from eating fleas. Fleas ingest tapeworm eggs and when your dog eats the fleas he eats the tapeworm eggs, too. They then happily hatch out inside your dog. A single tapeworm can grow to be four to six inches long in your dog’s intestine. The tapeworm’s head attaches to the intestine. As it grows it is followed by many little linked segments. These little segments look like rice. They break off and your dog passes them when he uses the bathroom. You can sometimes see them in his stool