Trivia: Aaron Taylor-Johnson was apprehensive about joining the cast due to Marvel's intense contracts and schedules. Even after signing on, he was extremely nervous. It wasn't until he found out his character's twin sister was being played by Elizabeth Olsen that he calmed down and really got excited about the project, as they are close friends and had previously played husband-and-wife in 2014's "Godzilla."
Trivia: Scarlett Johanasson was pregnant during filming, and thus had to rely on stunt-doubles moreso than usual. Amusingly, the three stunt-doubled hired to cover for her resembled her so greatly, the cast often would mistake the doubles for her and try to have conversations about the scenes and filming, only to realise they were talking to the "wrong" Black Widow.
Trivia: Joss Whedon desperately wanted to have a surprise cameo by upcoming Marvel Cinematic Universe heroes Captain Marvel and especially Spider-Man (who he had just learned was going to be rejoining Marvel) during the final scene where we see the new Avengers assembling to train, but he was unable to for time and logistics reasons.