The term 'sinuous swimmer' refers to two aquatic animals, an otter and an EEL. Otters are semi-aquatic mammals that are known for their playful nature and their ability to swim quickly and gracefully in the water. Eels, on the other hand, are elongated fish that are characterized by their snake-like movements and their ability to move through the water with ease. Both of these animals are considered sinuous swimmers due to their unique swimming styles.