This is based on the French graphic novel "Le Transperceneige". Director Joon-ho Bong discovered the comic in late 2004 during pre-production of The Host (2006), and was fascinated by the concept of people struggling on the train for survival.
The drawings in the tail section of Snowpiercer were illustrated by Jean-Marc Rochette, the original comic artist of the graphic novel Le Transperceneige.
Some children are taken away from the back of the train, and it is learned later from Wilford that small children are taken because they are the only ones that can fit into the sections of the engine that need repairs. This has been going on for years, yet the parents and others act as if this has never happened before.
At the end of the film, Curtis reveals that he killed Edgar's mother when he was still a baby. Presumably, Edgar is raised by Curtis, Gilliam and others in the back of the train. Edgar has a very strong Irish accent and yet, there doesn't appear to be any other Irish people around. If he was raised on the train since infancy, his accent should reflect those around him, the majority of which are American.
The following FAQ entries may contain spoilers. Only the biggest ones (if any) will be covered with spoiler tags. Spoiler tags have been used sparingly in order to make the page more readable.
Q
How much sex, violence, and profanity are in this movie?
A
For detailed information about the amounts and types of (a) sex and nudity, (b) violence and gore, (c) profanity, (d) alcohol, drugs, and smoking, and (e) frightening and intense scenes in this movie, consult the IMDb Parents Guide for this movie. The Parents Guide for Snowpiercer can be found here.