No less than nine writers worked on the script. Besides the credited writers Ted Elliott, Terry Rossio and David S. Goyer, work with also done by James Bonny, Richard Finney, Michael Engelberg, Neal Purvis, Robert Wade and the film's director, 'Stuart Orme. The final version mainly uses ideas from the Goyer and Orme rewrites.
For the seduction scene where Mary tries turn Sam back with one of her alien slugs, Julie Warner had to wear an apparatus that looked similar to her back with the creature's movements guided by a team of puppeteers and make up effects crew.
A lot of the scenes involving the meetings with Donald Sutherland and company were actually shot in Fresno, California. To which Keith David was not exactly thrilled to be working there stating "It's a good place to pass through, but working...no"
The hive or the Central Intellegence home where everyone gathers to collect intelligence from their human hosts was actually a set built on the Disney lot. While the actual entrance of the nest was at the Los Angeles County Center, with styrofoam walls built there to make it look like it was taken over.
At the start of the film when the boys are trying to convince Mary to go inside the fake spaceship, Andrew Nivens says, "She balked at Pirates of the Caribbean." Both Ted Elliott and Terry Rossio, two of the films credited screenwriters, went on to write the "Pirates of the Caribbean," series of movies.
Features cast members from similar-themed genre films: Alien (1979) (Yaphet Kotto), The Thing (1982) (Keith David), and Invasion of the Body Snatchers (1978) (Donald Sutherland).
When the slug has taken over a human, they immediately want to "merge" with one another. The tentacles form the shape of a human hand and interlock themselves with the other slug and stand to transmit information from one host to another and back to the central Hive.
Robert Heinlein's original book took place in 1997, which is also the same year that his other popular novel, "Starship Troopers" was released as a co-production by Sony and Disney under their Touchstone Pictures banner, which produced this film under their Hollywood Pictures banner.
Of all the films in Julie Warner's career, this film is the most popular despite the fact she was in the hit comedies "Doc Hollywood" and "Tommy Boy" with many of the films fans talking to her about it during Sci-Fi conventions when she makes appearances.
At the time of filming, Yaphet Kotto and Richard Belzer were the stars of the hit series "Homicide: Life On The Street"
Donald Sutherland and Eric Thal previously appeared in Six Degrees of Separation (1993).
In the French dubbed version Donald Sutherland's voice is dubbed by actor Jean-Pierre Cassel.
A few members of the cast that are apart of Donald Sutherland's group were featured on the TV series "Law & Order" during its 20 year run or the shows' spin-offs (Criminal Intent, Trial By Jury, Los Angeles and Special Victims Unit) with some playing recurring or different characters. These actors include Tom Mason, Gerry Bamman, Sam Anderson, Andrew Robinson, and even Eric Thal appeared on one of the series at one point. Richard Belzer would join the cast of Special Victims Unit, five years after this film would be completed.