Disney released a short featurette about the twins from Avengers: Age of Ultron, and the minute-long video includes a few neat tidbits about how the scenes with Ultron were filmed.
It sounds like a bit of a nightmare for the actors who had to work on those scenes. James Spader was on set to provide the voice and give everyone else something to use in their own performance, but Ultron's eyeline was shown by red dots on a metal rod a few feet over Spader's head.
Take a look at what that was like in practice. Spader acts directly to his co-stars in the scene, but they can't look back at him directly.
So Spader would be on set giving a nuanced, interesting performance as the titular villain ... and the other actors had to focus on something a few feet above him.
Blockbusters aren't easy, everyone.
Avengers: Age of Ultron will be available for purchase digitally on Sept. 8, and then the physical release will come on Oct. 2. You can read our review of the film to get caught up.