James Gunn was asked by a fan during his most recent Facebook Live stream if he would ever consider using Bradley Cooper as the "stand-in" for Rocket Raccoon in if the actor were available. Gunn quickly reminded those watching that Sean Gunn is a "motion reference actor." So not only is he used as a frame of reference for the other actors when performing scenes, but he's also delivering the lines that will later be spouted off by Cooper. More importantly, Sean Gunn is especially talented at handing the Rocket movements that not a lot of other actors may be able to pull off. So even if there was an opening in Cooper's schedule, Gunn will be sticking with Sean when it comes to the main Guardians of the Galaxy shoots. Sean has also acknowledged how difficult it is playing Rocket, as he said a few weeks ago that he has to stay in good shape or else he risks dealing with extra pain in his ankles, feet and ribcage.