Each of Devin's patients have names based on his own name: De-metrius, Vi-rginia, De-nis. This was done to enhance the idea that these 'people' are part of him and create a sense of familiarity. Celeste was given her different name to set her apart from the other similarly named people.
All of the characters names are of Latin origin.
In the set for Devin's office, a photograph of Daniel Hughes with his brother Jonathan Hughes on holiday in Lanzaroté when he was nine. There is also a photograph of his grandfather holding Jonathan Hughes as a baby.
The first draft of the short story was written in August 2010, and Daniel Hughes begun to adapt it to a screenplay in October 2010. The screenplay evolved very much from the original story, and even changed in places after filming had started. All of the characters names are different and the character of Celeste didn't exist in the original short story.
All of the people involved were 15 and 16 years old when production started. Then the average age increased when Shannon Sullivan, 17, joined as a crew member for some scenes.