Long in the tooth
There is an ancient Inuit story about a woman who fell into the ocean while holding a harpoon.
As the woman splashed about, a beluga whale swam up to see what was happening. The curious whale swam so close to the woman, it was speared by the harpoon. And that, the Inuit say, is how the first narwhal was made.
Narwhals live in the cold seas of the North Pole. Although scientists have studied them, they still have no idea what the narwhal's tusk is for.
What we do know is that narwhals have two teeth. In adult males, the right tooth grows into a big tusk. Occasionally the left tooth also becomes a tusk. Some females have tusks but most don't.
In the past, scientists thought tusks might be used for spearing fish. However, this turned out to be wrong.
Now they think male narwhals might use their tusks to battle rivals in underwater 'sword fights'.