NARRATOR: Tusks.

Nature's way of showing us a trip to the dentist could be far harder.

That's right.

Animal tusks are in fact overgrown teeth.

These continuously growing canines and incisors protrude beyond the mouth to become tusks.

And if you thought having a tooth coming out of your mouth was uncomfortable, imagine if the tooth also went through your skin.

Such is the luck of the narwhal and babirusa.

One of just two teeth, the narwhal's tusk is its left front tooth in a spiral that goes through its upper lip.

And if its shape and location wasn't special enough, its composition is unlike nearly any other tooth.

Where normally there is a hard coating of enamel or dentin, the narwhal tusk is soft and covered in nerves.

In other words, the tusk is built inside out.

These highly sensitive tusks may be used to detect chemical changes in the water around them, to find meals or mates, or the tusks, which many females lack, may be used in courtship rituals.

A distant relative of the narwhal, and the other animal with tusks that pierce through its skin, is the marvelous babirusa.

The males of this Indonesian wild pig are already known for having tusks grow from both their upper and lower jaws.

But it's their top canines that rotate to grow vertically up and through the snout that make them head, shoulders, and teeth above other tusk animals.

The babirusa tusks have actually been found to curve back into the skull in a few rare cases.

Though intimidating in appearance, babirusa tusks are fragile and not used for fighting.

And much like the narwhal, the function of babirusa tusks remains a mystery.

Yet for most tusked animals, the use of their long teeth is evident.

Tusks are a multi-purpose tool that help animals in their habitats.

They may be used for clearing away brush, gathering food, or self-defense, such as with the African elephant.

Or they may be used as ice picks, to haul heavy bodies out of the water, in displays of strength, and in more aggressive fighting over territory and females, such as the Pacific walrus.

And yet, even though having such a toothed tool is advantageous and potentially vital to survival in the wild, humans have turned having a tusk into a devastating liability.

People have long coveted ivory for its decorative and presumed magical properties.

Not only tusks from the elephant, but also walrus, warthog, and even the teeth of elk, hippo, and whale.

Thankfully, conservationists have worked closely with governments to prosecute poachers and dispel dangerous myths about tusks' medicinal powers, because for all tusked animals tusks serve far better purposes when left alone.

Whether those purposes are known or yet to be discovered.