Trivia: Denise Richards as a kid tells the boy that she'd rather be boiled alive than dance with him. She dies precisely that way later in the movie.
Trivia: Adam's girlfriend makes a reference to him being "no Angel". David Boreanaz, who plays Adam, plays Angel/Angelus on Buffy the Vampire Slayer and its spin-off series, Angel.
Trivia: The guy playing the corpse in the scene when Shelly is killed, is actually a good friend of the director Jamie Blanks.
Answer: If you remember, Dorothy kind of stumbled into her friend from around a corner before they both fell down the stairs. Adam could have quite easily forced her into the costume and then pushed her, making her seem like she was trying to attack her friend.