Trivia: Dr. Curt Connors, Peter's one-armed teacher in the film, is the man who will later become The Lizard, one of Spider-Man's longest running enemies.
Trivia: The two old men near the end, talking about it being "old school" are voiced by Frank Thomas and Ollie Johnston, two Walt Disney animators who worked on such classics as Bambi and Cinderella.
Trivia: The method by which Alice disposes of the zombie dogs (by throwing a flaming object into a gas filled kitchen) is similar to one of the numerous ways Jill Valentine defeats Nemesis in 'Resident Evil 3'.
Trivia: While filming the knife fight scene, Thomas Jane accidentally stabbed Kevin Nash.
Trivia: Due to the political situation in Iraq, the location for scale shots was moved from Morocco to Mexico, an ideal alternate choice with its broad beach. However, the rushed decision presented some obstacles. Coastal Mexico is an endangered turtle habitat, so to be granted permission to set up the Greek encampment and build boats on the large stretch of beach, the film crew implemented their own turtle incubation nursery, releasing a multitude of turtles while on location in Mexico. They also did not have an accurate idea of the physical conditions of that particular beach - it was unstable and 100 feet of beach washed away overnight, leaving Greek ships teetering precariously on the edge of the bank with the missing sand.
Trivia: The BPRD complex was (according to Del Toro) was originally FDR's secret emergency bunker. The library where Professor Broom dies was the president's office and Hellboy's room (with the big vault door) was his fallout shelter, just in case Germany perfected the A-bomb first.
Trivia: The band playing at the Bar Mitzvah is the same band from Old School who sung at Frank's wedding.
Trivia: Viggo Mortensen liked the horse that was used in the movie so much that he bought it.
Trivia: Before the film was released, N.A.S.A. sent a memo out to all of its employees stating that they were not allowed to comment on the likelihood of the events portrayed in this movie.
Trivia: Often times when a movie is distributed the name of the movie on the actual can is changed or altered to prevent piracy. The name on this movie was "Hal," a reference to "2001: A Space Odyssey" (1968).
Trivia: When Ben is talking to Riley in front of the Lincoln Memorial, you see a long pool behind them. This pool is filled with computer generated water, because the pool was drained at the time of shooting.
Trivia: The Chinese tattoo on Bill's arm reads Wo de shi jie, which means "My world."
Trivia: The "Montage" song is actually from an episode of South Park (Parker and Stone's TV show) called "Asspen," where Stan learns how to ski in a similar montage style.
Trivia: Ryan Reynolds gained 11kg (or roughly 24lbs) of muscle for his role as Hannibal King.
Trivia: The photo of Nicky in her confidential file is actually a promotional shot taken of Julia Stiles (Nicky) in 1999 for her movie "10 Things I Hate About You."