In this scene, we see Britanny becoming really aggressive in the washroom. At the same time, we hear a background voice explaining that Britanny has a disease called dissociative identity disorder. In fact, she has multiple personalities. She is transforming into Beth, the evil and violent side of her.
Scene 16 (W)
Are you doing well Britanny? You look... different.
The janitor (Anna) arrives in the washroom to clean it up. She is angry to see Beth there when she is not supposed to. Beth turns around and stares at her with a murderous look.
Scene 17 (CU)
Beth storms out of the washroom in direction of a classroom. Her friends are waiting for her there to steal the answer key to a math exam.
Scene 18 (W)
What just happened?
Beth enters into the classroom and her two friends immediately notice that she looks different and aggressive. She is staring at Florence with a scary smile.
Yes, I'm all right.
In this scene, we see Florence laying on the floor, dead. In the trailer, we don't know who killed her and how she died. Also, just before we see this grisly scene, we hear someone scream. (We can suppose that it's Florence.)
The janitor arrives out of breath and confused in the classroom where the scream came from. She is terrified because she finds the dead body of a student. She is trying to understand what happened to her. Anna asks the "question of our choice", to create intrigue. (What just happened?)