Jessica Alba spent several weeks at the New Mexico Commission for the Blind (NMCB) where she underwent a course with a specialized instructor, to better prepare for her role. She also spent a lot of time observing and hanging out with Jessica Bachicha, a blind soprano singer.
While filming at the University of British Columbia, Jessica Alba would often mess up her lines and, upon doing so, would systematically scream the "F" word at the top of her lungs. Eventually, the annoyed crew started echoing her screams throughout the building.
Jessica Alba particularly liked the fact that, according to her, the film is scary in a different, more subtle way than most other films in the genre, since "the audience is never sure if [her] character really is seeing things or if she's just losing her mind."
Just like the original Gin gwai (2002), the story takes its source from a real event, that of a young woman who committed suicide shortly after undergoing a cornea transplant, though she seemed to be living a perfectly normal and healthy life.
Jessica Alba declared that while she had been wanting to do a horror thriller for a long time, she did not want to do a slasher where each character dies in a more outrageous and bloody way, whereas she found this film to be elegant and very well-written, and her character, Sydney, to be elaborate and very interesting, thus enabling her to stretch her acting abilities.
The science that is depicted in the film, cellular memory, is in fact a real possible phenomena that is said to occur to organ transplant patients who inherit some form of memory or trait from their donor such as their personal interests, likes, or dislikes. It is theorized that this occurs due to humans having some form of psychic abilities to an extent.
Co-directors Xavier Palud and David Moreau liked the fact they "could really work on what was not obviously supernatural" and that "there were great opportunities to play with the audience's minds, to show them things that they couldn't determine were real."
This film is unique in the fact that it is the first western remake of an Asian horror film that is not Japanese but is in fact Chinese as every other remake that came out after The Ring (2002) was of a Japanese film.