Katie Jarvis, who plays Mia, had never acted before this film. A casting director spotted her having a fight with her boyfriend at a train station and offered her the role.
The film was shot chronologically, and the actors were shown only the part of the script they would be filming the following week - none of them knew what would happen to their characters later in the film.
Early in the film, Mia's little sister Tyler say to Conor "I like you.. I'll kill you last." This is a quote Arnold Schwarzenegger says in the 1985 film "Commando."
During the scene where Mia and Connor are going into the river to catch a fish, you can see the bruise on Mia's left arm from where her mum pinched her during her party the night before.