The following post contains minor SPOILERS for Avengers: Endgame. How have you not seen this movie by now? Come on, dude. Get with the program.

Any list of the coolest moments in Avengers: Endgame — or the coolest moments in any film of 2019 — would be incomplete without the fight between Captain America circa 2019 and Captain America circa 2012. Two Chris Evans occupy the screen together, and then beat the holy heck out of each other. It’s a seamless effect — so how did they do it?

This new video from Marvel reveals the secrets. Obviously Evans’ stunt double was involved — but it was even more complicated than you might have thought.

Watching the movie, I assumed the one Cap was wearing his helmet so that it was easier to replace the stunt double with Chris Evans, or to hide the double’s face completely without digital replacements. But no! The helmet was CGI, added in post-production because the version they shot, with two Chris Evans without masks, was more confusing and hard for audiences to follow. So they added a CGI mask. Wild! Moviemaking technology is almost as impressive as Stark tech.

Avengers: Endgame is available on home video now.

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