Playful marine mammal

SEAL

This flippered swimmer barks and balances balls on its nose at aquariums.

"Playful marine mammal" points to "SEAL" because seals are known for their energetic, almost dog-like behavior in water, often seen bobbing, diving, and interacting curiously with humans. The clue avoids trickery—it’s a straightforward definition, relying on common knowledge of seals as ocean-dwelling animals that appear playful. No wordplay or hidden meanings here, just a direct nod to their reputation as charismatic swimmers.