Warning: Spoilers ahead for "Game of Thrones" season seven.

In our weekly roundup of small details you may have missed, we noted the mysterious vision Bran had of the Night King and his army. The scene showed a bleak cloud making its way across the land. And in the center of the storm was the Night King, White Walkers, and thousands of wights.

While it's hard to tell exactly where the storm was, one detail seemed confirmed: The Night King was causing the storm.

In the books, Sam Tarly and other characters try to determine the answer to an important question: Do the White Walkers (or Others) appear when it's cold, or does it get cold when they appear?

Here's how Sam worded it in George R.R. Martin's books: "The Others come when it is cold, most of the tales agree. Or else it gets cold when they come. Sometimes they appear during snowstorms and melt away when the skies clear. They hide from the light of the sun and emerge by night ... or else night falls when they emerge."

The storm in the season seven premiere. HBO

Also in the books, Craster's wives (the group of Wildlings who live in a cabin beyond the wall) refer to this phenomenon as the "white cold."

Now, however, the show seems to have confirmed that the White Walkers are bringing cold with them, not just conveniently showing up when it happens to get cold outside.

We saw hints of this on the "Hardhome" episode from season five as well. When a White Walker entered a burning hut, he walked right through the flames. The fire seemed to cool to his presence, almost as if he were a walking fire extinguisher.

A White Walker in season five. Courtesy HBO

A similar effect happened in the season six episode "Home," when the Night King attacked Bran, Meera, Hodor, and the Three-Eyed Raven. The Night King and his ice cronies walked right through the line of fire that was holding back the wights.

But most of all, Jon Snow already said it best in the season six finale: "The true enemy won't wait out the storm. He brings the storm."

Read more about the small details you might have missed.

"Game of Thrones" season seven continues Sunday at 9 p.m. with "Stormborn."