Each of the lead girls had to undergo strict physical training which involved doing dead-lifts up to 96 kilograms (about 211 lbs.) several months before shooting. Vanessa Hudgens called that period "tormenting" and she broke down several times. In scenes where she's seen crying, she actually brought out moments from those sessions.
Emily Browning sang three of the songs featured in the film: "Sweet Dreams (Are Made of This)" at the beginning of the movie; "Asleep" which plays while Babydoll is crying in the bathroom; and she is featured on the track "Where is My Mind?" by Yoav.
Despite playing the lead character, Emily Browning does not have a line of dialogue until about eighteen minutes into the film.
According to director Zack Snyder, Emily Browning's character Babydoll (who is supposedly naive to guns) shows off way more experience with handling a gun than she should have. She had already received intense weapons training for the action scenes, and was unable to unlearn her prior experience for the opening scene.