See 39-Across

OTTER

Think of a playful, web-footed mammal that loves water and starts with the letter O.

This clue is a "see" reference, meaning the answer for this entry is fully explained at 39-Across. Since the answer is "OTTER," the solver would look to 39-Across for a definition or wordplay that leads to it—like a pun on "otter" sounding like "ought to" or a playful hint about the animal. Crosswords often use these cross-references to connect related clues without repeating information.