1. Justin Timberlake lost 15-17 pounds for his role as Sean Parker. He thought looking thinner would make him look younger
2. In an interview with Diane Sawyer, Mark Zuckerberg revealed that Jesse Eisenberg’s cousin, Eric Fisher, worked at Facebook.
3. In preparation for his role as Mark Zuckerberg, Jesse Eisenberg registered with Facebook two weeks before he began work on the movie. When the production wrapped, he canceled his account.
4. Every shirt and fleece that Jesse Eisenberg wears in the film is something that the real Mark Zuckerberg has worn.
5. After casting, David Fincher forbade principal actors from meeting their real-life counterparts until filming was completed. Justin Timberlake was the only actor who met his real-life counterpart, Sean Parker, during filming.
9. The opening breakup scene with Jesse Eisenberg and Rooney Mara took 99 takes.
10. In a scene where Mark Zuckerberg is taking art images from a Facebook profile to fulfill an Art History class requirement, the Facebook profile he is viewing is that of Tyler Durden, a character from another film directed by David Fincher, Fight Club.
11. Mark Zuckerberg originally planned on never seeing the movie.
12. Jesse Eisenberg and Andrew Garfield became good friends during filming. According to Eisenberg, the dramatic rivalry between their characters was hard for the two because it affected them emotionally.