A narwhal’s ‘horn’ is actually a tooth.

Some people think of narwhals as the unicorns of the ocean, as their protruding horns are similar to that of the mythical creature. But that distinctive feature isn’t a horn at all, but rather an elongated tooth that pierces its lip and typically grows to anywhere between 5 to 10 feet long. Narwhals use their lengthy tooths to hunt — not to pierce their target, but rather to whack and stun prey, making them easier to catch.

Narwhals only have two teeth to begin with, but typically only the left one grows long while the right one stays vestigial. Furthermore, males are often the only ones that have this prominent tooth. That said, there are rare instances in which females develop a long tooth of their own, and other cases — for both males and females —- wherein both teeth grow out to form two lengthy tusks.