Hi, thanks for your question. A rice-shaped worm in the stool is most likely a Tapeworm segment. Tapeworms are common, and are most commonly caused as a result of swallowing an insect, lizard, or other small "critter". Fleas are the most common insect involved in tapeworm infection. Your veterinarian can prescribe a dewormer medicine to treat these tapeworms, and if fleas are present, these must be treated as well.