Trivia: Stan Lee makes his customary appearance when Rocket Raccoon is sweeping the plaza for likely targets - he is seen chatting up a young lady. (00:16:00)
Trivia: Director Martin Scorsese makes more then just a cameo in this film, he's the passenger that sits with Travis talking about how he's going to kill his wife for cheating on him with a black man. He's credited as "Man Watching Silhouette".
Trivia: Wade Wilson is on the "Dead Pool", seen briefly at the back of the bar, but so are various celebrities, such as Bill Cosby, Kanye West, and Charlie Sheen. Perhaps most notable are Ryan Reynolds and TJ Miller, stars of the movie.
Trivia: Stan Lee makes his usual cameo, this time as a patient at the asylum where Selvig is being held.
Trivia: Kate Beckinsale's mother makes a cameo as a vampire in David's covenant. (00:33:20)
Trivia: In the opening musical sequence when they jump out of the pool, the lady behind Austin can be seen laughing because her swim hat has fallen down.
Trivia: When Quasimodo is singing a few minutes into the film, he is standing above the town street where people are walking around, doing business. If you look closely to the lower right of the scene, you can see Belle from "Beauty and the Beast" reading a book in her blue dress, walking.
Trivia: Anthony Stewart Head (of "Buffy the Vampire Slayer" fame) makes a cameo as the man who congratulates Sweeney after his competition against Signor Pirelli. Head originally had a larger role, but his scenes were eventually cut out. (00:38:25)
Trivia: While Lin (played by Jackie Chan) is in disguise and working in his daughter's school cafeteria, his name tag shows Jackie Chan. (00:31:25)
Trivia: Not a mistake, just something that's not immediately obvious: When they arrive at the plane after the club scene, the man that walks them to the plane is Dan Aykroyd.
Trivia: Stan Lee, who co-created the Hulk, and Lou Ferrigno, who played him in the 70's TV show, have cameos as a pair of security guards in the beginning of the film. Ferrigno later made another cameo as a security guard in the 2008 reboot.
Trivia: At various points in the film, Jack Nicholson flicks his eyes to the camera, often only for a few frames, frequently hard to catch. It's deliberate - in one clip of behind the scenes footage Kubrick lies under him while setting up a scene, and specifically tells him to look down to the camera when filming. But there's no specific answer as to why - genre-defying, or to make the audience feel more threatened, or to make the viewers feel like the ghosts he sees. Hard to unsee though.
Trivia: The infant playing Connie and Carlo's baby son Michael Francis Rizzi who Kay holds during the christening scene is Sofia Coppola, Francis Ford Coppola's daughter, who was born in May 1971. Sofia later had a prominent role in Part III as Michael's daughter, Mary. Other than the main characters, Sofia is the only actor to have appeared in all three films. In The Godfather II, she can be briefly seen as an immigrant girl on the ship that brings Vito Corleone to Ellis Island.
Trivia: John Cusack's real-life sister, Joan Cusack, is wearing a neck brace on the bus at the beginning of the film.