Renowned astronomer Seth Shostak was hired as a consultant on the film. He reviewed the script several times for errors, and gave suggestions for making the scientists less dry: "Real scientists don't describe an object entering the solar system as 'notable for the fact that it was not moving in an asteroidal ellipse, but moving at nearly 3*10 to the 7 meters per second'. More likely, they would say that there was 'a god-damned rock headed our way!'" He also noted the scientists should refer to one another by a first name basis.
In Harry Bates' short story "Farewell to the Master", upon which the movie is based, the last line revealed a dramatically different angle. It reads: "'You misunderstand,' the mighty robot had said. 'I am the master.'"
Keanu Reeves recorded the line "Klaatu barada nikto" twice, and one recording was played backward and spliced with the other (which was left normal) to make the overall dialogue sound more otherworldly.
According to the filmmakers, John Cleese was the most difficult choice in casting, as he was primarily noted for comic roles. Cleese felt that at his age, a dramatic role with subtle humor would be an easier role to play, rather than another manic old man.
The line "Klaatu barada nikto" from The Day the Earth Stood Still (1951), was re-used in this film at Keanu Reeves's insistence. In both films, the line is used to stop Gort from attacking the humans. It is also the same phrase that Ash from Army of Darkness (1992) must say before he removes the Necronomicon.
The design of GORT is similar to his original portrayal in The Day the Earth Stood Still (1951), but GORT is now a biological form, rather than mechanical, as Scott Derrickson considered some extraterrestrial races would develop advanced biological forces, instead of technology.
The military group guarding the base where GORT was being analyzed is Whiskey Task Force. Presumably, it was specially created for dealing with unknown threats by someone with a sense of humor, giving it the initials WTF.
The orb was supposed to be filled with white limbo light, but Director Scott Derrickson felt the concept would then be unoriginal, and changed the color to greenish, a more appropriate color for an environmentally conservative race.
Klaatu uses the phrase "tipping point", which is a climatological term meaning the point at which the reversal of climate change becomes impossible. Some scientists believe that this has already happened.
When Javon is watching television at Professor Barnhardt's house, it shows various pictures of riots from around the world. One shot shows actual riot footage from Serbia on October 5, 2000, the day Slobodan Milosevic was overturned. A large crowd is in front of Serbian Parliament. Smoke is visible, because part of a building was on fire.
As part of the German (and probably too in other countries) promotional campaign, advertisements changed the title of the film to include the name of the city where the ads were published (for example, "The Day Cologne Stood Still").
The words "Klaatu Barada Nikto", which are in the original 1951 film, spoken by Helen Benson to GORT the robot, has featured in many other productions, for instance, in Army of Darkness (1992), Ash must speak it, to stop the undead army from appearing.
This movie is rich with Oscar winners and nominees, directly or indirectly associated with this movie. A quick glance reveals; John Cleese for A Fish Called Wanda (1988) (Nominated); Jennifer Connelly for A Beautiful Mind (2001) (Won); Kathy Bates for Misery (1990) (Won); and Edmund H. North (original 1951 screenplay) for Patton (1970) (Won).
In the final scene, the Sydney Opera House and Sydney Harbour Bridge can be briefly seen from the point of view of Mrs. Macquarie's Point - the same park used for the final scene of Keanu Reeves's other science fiction apocalypse story, The Matrix Revolutions (2003).
The initial description of the ship in the briefing near the beginning, is very similar to the way Rama, in Rendezvous with Rama (2003), is initially described, including the name of the Agency that detected it, and the manner in which the object was moving.
The coordinates for the "impact location" that appears on the big screen (Latitude 40.75136, Longitude -73.98712) falls on the The Haier Building, 1352-1362 Broadway Avenue, at the corner of West 36th Street, in midtown Manhattan. The building used to be the headquarters of the Greenwich Saving Bank from 1833 to 1981.
The trivia items below may give away important plot points.
GORT's trademark eye beam is used twice in the movie. The first time, to cause all electric to go out in the area, when Klatuu is shot in the beginning of the movie, and the second time to destroy the two drones, and the sidewinder missiles, that they launched to try to destroy him.
Klaatu used the famous line, "Klaatu Barada Nikto" twice in the movie. At the beginning, after he is shot by the military, to stop GORT from hurting them, and then at the end of the movie, when Klaatu touches the sphere and says, "Klaatu Barada Nikto" to stop GORT, who now is in the form of the Nanobots, from destroying the world. Once he touches the sphere and says, "Klaatu Barada Nikto", the nanobots all die.
In the original, Klaatu instructed Helen to say the famous line "Klaatu Barada Nikto" to GORT in the event of his death, which she did. In this film, Klaatu himself says the famous line to GORT shortly after arriving on Earth, after being shot by the Army.