Scientists don't know exactly why narwhals have tusks—though they might be used to impress females or fight other males. But tusks are more than battle swords—they're packed with nerves and covered in tiny holes that allow seawater to enter. This gives tusks a sensitivity that could help narwhals detect changes in their environment such as temperature or even the water's saltiness. Clues like these might help narwhals find prey or survive in other ways.