While working on “The Avengers,” Whedon shared that at first the possible interactions between the characters are “just extraordinary fun”; however, once getting “into the practical stuff, like ‘How does this guy...’, it’s a nightmare.” Whedon added, “It’s really a recurring nightmare because it was so much like ‘Serenity’ in that way. So I really sort of went ‘Oh, God, I’ve done it again!’”