Spoiler alert: This post contains mega spoilers for the latest episode of Game of Thrones, “Beyond the Wall.” If you haven’t seen it yet, go watch it and then return faster than a raven flying over plot holes.

As Game of Thrones races towards it seventh season finale, revelations and theory confirmations are coming at us as fast as a raven headed for Dragonstone. We still aren’t sure what’s in store for us in “The Dragon and the Wolf,” but we now know–for certain–how dragons in GoT lore breathe fire.

During the surprisingly emotional climax of the penultimate episode, “Beyond the Wall,” Daenerys’ dragon Viserion is struck in the neck by a frigid spear thrown from the Night King’s icy claw. When the spear makes the fatal blow, there is a notable explosion of both blood and fire. It’s that explosion that confirms dragons on the show (more technically, wyverns) breath fire by expelling a pressurized gas, likely methane or some other volatile organic.

The reason is chemistry. Unlike what you’ll see in the movies, not everything that’s flammable is always explosive. It matters how that flammable substance is interacting with the elements around it. For example, if you throw a match into a bucket of gasoline (don’t), it wouldn’t explode. The gasoline needs a certain amount of oxygen to ignite, and so only the surface of the gasoline, where the vapor is mixing with the air, would be set ablaze. This stoichiometry–the calculation of relative quantities of reactants and products in chemical reactions–is the reason why gasoline is aerosolized in your car engine. It wouldn’t ignite otherwise.

When Viserion’s neck erupts in flames, the same process is taking place. The spear must be piercing wherever the pressurized gas is held, which, because of that pressure, pushes itself into the surrounding atmosphere. Now in a ratio with oxygen that allows for combustion, the fire already in the air around Viserion ignites the gas evacuating the puncture, and there’s a conflagration. Poor dragon.

And though we know the show uses liquid fuel-based flame throwers when practical flames are needed, the demise of Viserion almost perfectly matches what the chemistry dictates if a normal butane lighter is pierced. The pressurized butane gas pushes itself out as a dangerous, expanding plume, and once the mixture is right, it ignites.

And if you go back and look closely, you can see Game of Thrones‘ dragon design includes a large sack at the base of the neck. That could easily accommodate hydrocarbon gases built up from the animal matter decaying in their cavernous guts. This seems like the most likely explanation, though the spear also could have pierced the neck in such a way as to redirect some of the fire out of the wound, or what was escaping the wound could have been certain hypergolic chemicals.

Hey, anything makes more sense that Varys being a merman.

Images: HBO

Need More Thrones Before the Season Finale?

• Breaking down the controversial Bran/Night King theory.
• How fast those Dragons really had to fly in “Beyond the Wall.”
• What can we learn from the Season 7 finale photos?