- Castor and Pollux are the twins from the constellation Gemini, the twins. On the opposite side of the star calendar is Sagittarius, the Archer.
- Castor and Pollux's last name is Troy, referencing the Trojan Horse, which is effectively what the face transplant surgery turns Castor and Archer into.
- The blood types for the two main characters (i.e. Sean Archer and Castor Troy) are mentioned in the movie, and at a subtle level they reflect their antagonistic nature. Archer's Blood type is O negative, while Troy's is AB positive, these two blood types are as different as you can get. O negative (the universal donor), reflects Archer's role as a policeman dedicated to serving the community, while Troy's AB positive (the universal recipient) suggests someone who takes from society without giving anything back.
- If Troy and Archer have differing blood types and this fact is a plot point in getting Archer's wife to realize Archer is Troy, how come Archer's body didn't reject Troy's face when it was put on him?
- How does his wife not notice his penis is different? Something brought up by many critics, including Roger Ebert.
- It's implied that the couple haven't been having sexual relations for a while. Beyond that they two may not have that different a penis. It's not exactly a one a kind part.
- An early draft of the script had a line stating that Castor and Archer had virtually identical body types and, yes, penis sizes. While the line isn't in the film, I imagine the idea must have still been in mind.