OK so narwhals, the unicorns of the sea, have been swimming around with a mystery strapped to their faces this whole time, and scientists just cracked it. Their tusk, which is actually a giant tooth and the longest tooth in the entire animal kingdom, is famously straight. Like suspiciously straight. Like who-gave-you-a-ruler straight. And per the new research over at Phys.org, narwhal tusks are the only straight tusks found anywhere in nature, and now we know how they pull it off.

Quick refresher before the new stuff: the tusk is a left canine tooth, usually, that grows out through the lip and can reach more than two meters, so about 6.6 feet, over the whale's lifetime. And it's covered in a spiral, which you'd think would make it curve. Spiral things curve! That's kind of their whole deal! But the narwhal tusk stays dead straight, and the secret is that the tusk basically engineers itself as it grows. The structure inside contains two opposing spirals, one twisting right and one twisting left, and they counterbalance each other so the natural tendency to bend cancels itself out. The tooth is doing math all by itself. I can't stop thinking about that part.

And it's not a subtle process either. The growth pattern is consistent enough that the tusk resists curving even though everything about its shape says it should. Every other long tooth in nature, think elephant tusks, warthog tusks, walrus tusks, curves. Narwhals are the only ones out here growing a laser-straight spear off their face, and now we know why.

What gets me is how long we've shared the planet with these animals without knowing this. Narwhals have been diving under Arctic ice for their whole existence and we only just now figured out the physics happening inside their faces.

Also the answer to one of the ocean's prettiest mysteries turned out to be a tooth doing structural engineering, and I love that so much. The explanation is somehow more delightful than the mystery. The tusk isn't straight by luck. It's straight because two spirals inside it are quietly, continuously canceling each other out as it grows, which, same, tusk. Same.

Joy is worth documenting, and this one comes with a spiral. Two, actually.