If you haven't seen last night's premiere of "Game of Thrones," stop reading this. Mild spoilers ahead.

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So on last night's Season 7 premiere of "Game of Thrones," lots of stuff happened. The Red Wedding was repaid with the Red Wine Tasting. Ed Sheeran made a cameo. Cersei remodeled her patio with some cartographic artwork. Jon Snow released a BOM for his upcoming line of White-Walker-killing products. And it was revealed that Sam, who's been hanging out in that bad-ass library in the Citadel, discovered where there's a cache of the material at the top of Snow's BOM, "dragonglass."

We HBO-watching earthbound humans recognize dragonglass as obsidian. In the mythical world of Westeros, if fashioned into blades it can be used to kill those pesky albino zombies. But here on earth we use it to make everything from jewelry to sex toys*.

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So what exactly is obsidian?

In both worlds, in comes from lava or more specifically, molten magma. It's essentially naturally-occurring glass. Way before we humans figured out how to work metal, obsidian was the go-to material for creating edged weapons because the stuff is freakishly sharp.

How sharp? So sharp that some surgeons (outside of America, that is) actually use scalpels made of obsidian to perform surgeries. Obsidian is not crystalline in structure, whereas steel is. That means that if you look at the blade of an obsidian scalpel next to a steel scalpel under a microscope…

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…you can clearly see that one is sharper than the other. According to CNN,

Dr. Lee Green, professor and chairman of the Department of Family Medicine at the University of Alberta, says he routinely uses obsidian blades.

"The biggest advantage with obsidian is that it is the sharpest edge there is, it causes very little trauma to tissue, it heals faster, and more importantly, it heals with less scarring," he said.

"It makes for the best cosmetic outcome."

He explained that steel scalpels at a microscopic level have a rough cutting edge that tears into tissue, a function of the crystals that make up the metal. Obsidian, meanwhile, cleaves into a fine and continuous edge when properly cut.

Obsidian scalpels are a no-no in America because they don't have FDA approval. They're also quite brittle and don't tolerate lateral forces well, and understandably some surgeons don't want to use a scalpel that might break off inside the patient's tissue.

On Westeros, however, it might be acceptable to break blades provided they're inside the body of a White Walker. Particularly if Sam's information makes it to Jon, and if Jon can acquire the mining rights to the dragonglass cache on Dragonstone. Hopefully we'll know more next week.

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*For those of you that thought I was joking, here's a bunch of obsidian dildoes.