the digestive system is a part of an animal
mammal_digestive_tract is not body_part. mammal_digestive_tract is body_part. bird_digestive_tract is body_part. mammal_rib_cage is body_part. digestive_system is system. mammal_digestive_tract is digestive_tract. all_animals has digestive_system digestive_tract is organ_system. digestive_tract is body_part. all_animals has not digestive_system