Adam Pearson, who plays the disfigured man who is lured into the vehicle, broke his leg when he was struck by a cab on his way to audition for his role. Director Jonathan Glazer auditioned him the next day at the hospital and gave him the job.
A paparazzi still of Scarlett Johansson, in character, falling down became a wildly popular Internet meme in which users would Photoshop Johansson into various situations. As the scene was shot with hidden cameras, it was not until the movie's release that it was revealed the fall was intentional.
The film took nearly 10 years to be made, and one of the early drafts of the scripts included a Scottish married couple, who were revealed to be aliens in disguise. Brad Pitt was, at the time, cast as one half of the couple.
Close to the end one of the motorcycle riders overlooks a valley shrouded in fog. The composition of the image and the pose of the rider mimics Caspar David Friedrichs 1818 oil painting Wanderer above the Sea of Fog.
Jonathan Glazer did not want to use make up for the man with neurofibromatosis. Adam Pearson was cast after the production team contacted Changing Faces, a charity supporting people with facial disfigurement. His ideas about how Scarlett Johansson character could seduce his character were added to the script.
One of the locations where Under the Skin was filmed was in the Robert Street area of Port Glasgow. (Where the second victim is lured). Filming had to be delayed for a number of days as there was a real life murder in the next street prior to filming and the Police had cordoned the area off.
The nightclub that Scarlett Johansson gets pulled into is Club Earth in Livingston, West Lothian. Although the exterior shots & many of the interior shots are of the actual club, her escape route & scene in the toilet corridor seem to have been filmed elsewhere.
The trivia item below may give away important plot points.
One theory suggests that The Female is actually a Selkie instead of an alien. Selkies are mythological creatures found in Scottish, Irish, and Icelandic folk lore. Selkies are said to live as seals in the sea but shed their skin to become human on land. Selkies are described as being very beautiful in their human form and therefore having great seductive powers.