The term 'playful mammal' can be summarized by two crossword solutions: otter (5 letters) and SEAL (4 letters). Otters are semi-aquatic mammals that live in rivers, lakes, and oceans. They are known for their playful behavior, such as sliding down muddy banks and playing with rocks. Seals are also semi-aquatic mammals that live in the ocean. They are known for their playful behavior, such as swimming in circles and playing with objects in the water.