At this point most fans of the Marvel Cinematic Universe know that Sean Gunn does double duty in the franchise. He plays both the Ravager named Kraglin in the Guardians of the Galaxy movies, directed by his brother James Gunn, but he also handles the on-set work for the digital creation that is Rocket.
Of course, the fact that Rocket is less than half the size of a normal adult human means that a lot of what Sean Gunn ends up doing on set looks...well, more than a little ridiculous. His brother James posted a brief clip form one of the special features for Avengers: Endgame, which shows our heroes marching together in one of the film's biggest moments, complete with Sean Gunn trying to move while crouched down to the size of Rocket. And yes, it's hilarious.
The shot is all pre-digital effects. Everybody's wardrobe is covered in markers where their time travel suits will be created over their costumes. But then, next to Robert Downey Jr., we see Sean Gunn walking partially on his hands so that he can keep his balance.
While James Gunn's post is absolutely meant to poke some fun at his brother, that's what brothers do, that's not the only reason he's included the clip. The director also wants to correct a misconception that Sean Gunn's only purpose is to act as a stand in, so actors have something to work against. While Sean Gunn isn't doing straight motion capture, his acting and facial expressions are used by the digital effects artists when it comes to creating Rocket in post-production.
I think, after watching this clip several times, that every actor in the MCU should be commended for the work they clearly do keeping a straight face while filming these movies. I'm not sure I could deliver lines opposite Sean Gunn without breaking out into hysterics. I'm not sure how Sean Gunn himself is able to keep it together.
James Gunn says that watching his brother perform Rocket is always hilarious, so it's quite possible that other actors do have some difficulty at times. The new Blu-ray for Avengers: Endgame does include a gag reel. What are the odds the entire thing is just people laughing as they try to deliver a serious and emotional moment opposite a guy crouched down into a ball?
One assumes we'll get lots more of Sean Gunn in the MCU in the future. While Guardians of the Galaxy Vol. 3 is currently without a release date, the movie is coming. This means we'll get lots more of Sean Gunn in both his roles, the one we can see, and the one we can't, except for hilarious behind the scenes clips.
Avengers: Endgame is out today in Digital HD, so you can now experience both the before and after of Sean Gunn's performance as Rocket, combined with Bradley Cooper's voice. The movie hits Blu-ray August 13.