Episode 4 (‘The Spoils of War’) of season 7 of Game of Thrones features one of the most exciting battles of the entire series so far. Known as the ‘Loot Train Attack’, the battle sees Jaime Lannister’s ground forces receiving the brunt of a fiery attack from Daenerys Targaryen, who is riding her dragon Drogon.

The sequence includes an impressive array of practical fire stunts, digital armies and set extensions, and of course a CG dragon. But it was one small touch added by the visual effects team that caught the attention of many viewers. This is the brief moment that Drogon’s wing, as the dragon makes a run above a stream towards the battle, neatly clips a tree on the river bank.

It’s a small thing, but a hallmark of the attention to detail that is part of the visual effects in Game of Thrones, led by visual effects supervisor Joe Bauer and visual effects producer Steve Kullback. Here, Bauer explains to vfxblog how fellow visual effects supervisor Eric Carney, along with Iloura and Image Engine, made that very cool shot possible.

Joe Bauer: Well, Eric Carney was our supervisor on the ground in Spain where that was shot, because we were prepping all the big sequences to come and future episodes. He was our man executing all of our planning on the set.

That coverage was done with a drone, and I know they had some technical issues when they got out there. We had quite a few tries to get the nice steady plates, and ultimately we did. And then really it was a matter of putting the dragon model into the scene. First of all, it involved 3D tracking the footage, and then putting the dragon model in and realising that the wings would bisect a tree. So the shot was really just out of necessity.

We had a LIDAR scan of the area, which is a digital model of the whole environment in the planning stage, but then the blocking sort of evolved in the shooting when they got there. The dragon ended up further up the stream that was feeding the little lake. Ultimately, we just had to deal with that tree.

Iloura made a digital branch and Image Engine was responsible for the dragon. It goes by in very few frames, but it’s interesting that people noticed that. We thought we were being quite clever disturbing the water underneath the dragon. I guess either people accepted it, but that was a complete contrivance, too, because you’d have to break the sound barrier, I think, before the water would behave that way.

Anyway, we’re a bunch of geeks and fans too, and anything cool that we can imagine or think of cramming into any sequence, we tend to go for it.

Below, watch the featurette released by HBO that focuses on the Loot Train Attack.