30 things you probably didn't know about 'Inception'

• Christopher Nolan's mind-bending science fiction film "Inception" premiered 10 years ago. 
• Because many audience members were left perplexed by the film's abstract concepts and multi-leveled time warps, they missed some of the details Nolan included in the film.
• From hidden symbols to behind-the-scenes secrets, Insider rounded up 30 details that you probably didn't know about "Inception."
• Warning: This post may contain spoilers about "Inception."
• Visit Insider's homepage for more stories.

An exploration into the world of dreams (namely, dreams within dreams), Christopher Nolan's "Inception" left audiences bewildered when the film was released in 2010. 

"Inception," both fast-paced and visually stunning, follows Dominick Cobb (Leonardo DiCaprio) as he and his team enter their targets' dreams to extract and implant information.

The line between reality and dreams becomes nearly indistinguishable as the characters delve deeper into their subconscious, at times making the audience wonder whether they're watching a moment unfold in the real world or within someone's mind. 

The ambiguous concepts, dream layers, and allegiances in "Inception" can be overwhelming to piece together upon first watch, making it easy to overlook the subtle details and hints that Nolan has placed throughout the movie. 

Insider rounded up 30 details and behind-the-scenes facts that you probably didn't know.

SEE ALSO: Every single Christopher Nolan movie, ranked by critics

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Christopher Nolan thought of the idea behind "Inception" when he was 16, and the script took him 10 years to write.

Nolan had been fascinated with the nature of dreams for a long time before writing "Inception."

"I wanted to do this for a very long time, it's something I've thought about off and on since I was about 16," he told The Los Angeles Times. "I wrote the first draft of this script seven or eight years ago, but it goes back much further, this idea of approaching dream and the dream life as another state of reality."

When he did begin to work on the movie, it took him a decade to finish the script. 

"The final piece of the puzzle for me with the script I'd been trying to finish for about 10 years was figuring out how to connect emotionally with the central character in a way that would make it a more emotional story," he told Deadline. 

During several interviews, Nolan has explained that he began writing "Inception" as a heist film but changed it as he views the genre as "deliberately superficial" and lacking in emotion.

The movie barely used any CGI for its effects.

Rather than relying on CGI to bring Nolan's vision to life, the team used FX shots by combining live action with digital animation, visual effects supervisor Paul Franklin told Wired. 

Visually stunning moments like the city of Paris folding over itself and Arthur fighting projections in a zero-gravity rotating hallway were shot using visual effects. 

"Using CG versions of complicated action like falling buildings, explosions or certain lighting effects are all predetermined by the nature of the software and the ideas that went into it. In the effects world, there's still a lot of useful randomness in real-world physics," Franklin explained.

The limbo scene, with large buildings falling apart on the beach, was the most difficult scene to create, according to Franklin. 

"For a long time we just couldn't get it right – we'd end up with something that looked like an iceberg version of Gotham City with water running through it," he said. 

They based the model off of a glacier, and a designer filled in the gaps with the architecture seen in the movie. 

"It was just a matter of methodically adding in elements like roads, intersections, and ravines until we ended up with this extremely complicated (but organic-looking) cityscape," Franklin explained. 

They considered making "Inception" 3D but decided against it.

Due to time constraints and concern over the quality of the finished product if rushed, the "Inception" team decided not to make the film 3D, Nolan shared during a Warner Bros. press conference. They did consider using the technology and even tested it while editing the film. 

"When I really looked at the time period we had and where my attention needed to be in finishing the film, I decided that I didn't have enough time to do it to the standard I would have liked. I think the question of 3D really is one for audiences in a sense. The tests we looked at, it's perfectly possible to post-convert a film very well," he said. 

Nolan added, "I like not having glasses when I watch a movie and I like being able to see a very bright, immersive image. So I think at the end of the day, I'm extremely happy to be putting the film out with 35 mil film prints very brightly projected with the highest possible image quality. That's really what excites me."

Edith Piaf's song "Non, Je Ne Regrette Rien" hinted at the film's major themes.

Cobb's team used the French song "Non, Je Ne Regrette Rien," which translates to "No, I Don't Regret Anything" in English, as a "kick" to signal that it's time to leave a dream.

The lyrics translated in English, "No, absolutely nothing / No, I regret nothing / It is paid, done, forgotten / I don't care about the past," may allude to Cobb and Saito's recurring line: "Do you want to become an old man, filled with regret, waiting to die alone?"

The song is also a direct contrast to Cobb's inability to let go of his late wife, Mal. 

"With my memories, I light the fire / My pains, my pleasures / I don't need them anymore / I'm done with the loves and all their troubles / I'm done forever / I start over with nothing," Piaf sings, hinting at Cobb's hypocritical advice to Ariadne, telling her to avoid using personal memories while building dreams. 

Hans Zimmer created the film's score by manipulating one beat from Piaf's song.

After "Inception" was released, a fan made a video pointing out the similarity between Zimmer's score and a slowed-down version of Piaf's "Non, Je Ne Regrette Rien."

Because time passes slower in each layer of a person's dream, it would make sense that the French track, played in real-time, would be stretched out to signal the time warp inside of a dream.

Zimmer told The New York Times that the use of Piaf's song in the score "wasn't supposed to be a secret."

The score isn't exactly a slowed-down version of the song, however. Instead, Zimmer said he took one beat from "Non, Je Ne Regrette Rien" and manipulated it. 

"I had to go and extract these two notes out of a recording," he said. "I love technology, so it was a lot of fun for me to go and get the original master out of the French national archives. And then find some crazy scientist in France who would actually go and take that one cell out of the DNA."

Zimmer explained that "all the music in the score is subdivisions and multiplications of the tempo of the Édith Piaf track. So I could slip into half-time; I could slip into a third of a time. Anything could go anywhere. At any moment I could drop into a different level of time."

Nolan almost cut "Non, Je Ne Regrette Rien" after he cast Marion Cotillard, who coincidentally starred as Piaf in "La Vie en Rose" years prior.

Nolan included Piaf's song in his script long before he cast Cotillard as Mal.

Coincidentally, the French actress won an Oscar for her performance as Piaf in "La Vie en Rose" (2007) prior to landing the "Inception" role. 

Because of Cotillard's association with the singer, Nolan almost cut the song from the movie, Zimmer told The Los Angeles Times. Zimmer, who used the song to shape the film's score, said he convinced Nolan to keep it in the film.

The film was shot in six countries.

The cast and crew traveled to a total of six countries while filming "Inception."

Locations included the U.S., Morocco, Canada, France, the U.K., and Japan. 

Joseph Gordon-Levitt said the scene in the hallway was both the most fun and the most painful experience he's ever had on a set.

In the second level of the Fischer extradition mission, Arthur sprints down a revolving hallway to get away from the projections.

Though there was a stunt team on set, Gordon-Levitt took on physical training and combat practice two weeks before shooting to do the zero-gravity fight scene himself. 

"It was just about the most fun I've ever had on a movie set. It was also, probably, the most pain I've ever been in on a movie set, physically, but you know, pain in a good way, like in the way I guess athletes must get when they have to put on their pads and they tape up their ankles and they get a little beat up throughout the day, but that's just part of slamming yourself into walls and jumping around all day," he said during a Warner Bros. press conference. 

More than 500 crew members made it possible to shoot the iconic scene, which took place in a 100-foot revolving hallway.

Nolan's son Magnus played James, Cobb's son.

The filmmaker's son Magnus portrayed James, Cobb's 20-month-old son. As of 2020, "Inception" remains his only film credit.

Christopher Nolan also cast his cousin, Miranda, as a flight attendant.

Miranda played the flight attendant serving the first-class passengers on the plane to Los Angeles in "Inception."

She's also appeared in minor roles in Nolan's other films including "The Dark Knight Rises" (2012) and "Dunkirk" (2017).

Before Ellen Page knew about "Inception," she met with Nolan as a fan of his work.

The actress plays Ariadne, an architecture student brought onto the team to build dreams. Before she even knew about the film, she met with Nolan as a fan. 

"I actually had a general meeting with Chris, because I'm a huge fan of his films. I didn't know about 'Inception' when I met him. I really liked him — such a down-to-earth guy, no ego at all, just a pleasant, enjoyable guy to talk to," she told MTV.

Page said she didn't view the meeting as a gateway to a project but received a call a week later. 

"The idea of 'Inception' came up and that he was thinking about me for it. Then I got to read the script in an office. I wasn't sent a copy. The script totally blew me away," she said. "I was totally into playing the character, and he decided I was right for the part."

Nolan incorporated a painting by Francis Bacon, his favorite artist.

When Mal and Cobb are speaking in the Japanese castle during the Saito extraction job, a Francis Bacon painting titled "Study for Head of George Dyer 1967" hangs on the wall.

The painting of Dyer, who was Bacon's lover from 1963 to his death in 1971, shows a distorted version of his face containing a gaping hole. The work is one of many that Bacon created of Dyer, both during his life and after his death. 

For Nolan, who told Tate that he turns to art when unable to express himself with words, the painting's placement is no mistake.

"I think there are, for me, suggestions of distortions of memory in the way faces are portrayed in a way that I found fascinating in various ways. In my work I've tried to echo or represent it cinematically," Nolan said of Bacon's work. 

Later in the film, the audience finds out that Mal, who stares directly at the painting before turning and speaking to Cobb, is a mere projection of the protagonist's memory.

Like Bacon's misshapen image of Dyer, Nolan is showing Cobb's imperfect, distorted version of his wife, standing directly in front of Bacon's work.

The number shown on Arthur's totem reappears several times in his dream.

Arthur's totem, an object that signifies whether or not he's in a dream or reality, is a red pair of dice.

When he shows it to Ariadne, the side with five dots faces the camera. In his dream at the hotel, the number appears several times. 

The hotel has at least five floors, and two "5" signs frame Gordon-Levitt several times during the zero-gravity fight scene. 

The snow fortress in Eames' dream is nearly identical to the Geisel Library in San Diego, California.

The snow fortress in Eames' dream closely resembles the Geisel Library in San Diego, California. The library, constructed using glass and concrete, was designed in the late '60s by famed architect William Pereira.

Nolan hasn't confirmed that the fortress was modeled after the Geisel Library, though he has spoken about his appreciation for architecture and its influence on his films.

"I'm very interested in the similarities or analogies between the way in which we experience a three-dimensional space that an architect has created and the way in which an audience experiences a cinematic narrative that constructs a three–dimensional reality from a two-dimensional medium—assembled shot by shot. I think there's a narrative component to architecture that's kind of fascinating," he told Wired. 

The license plates in Yusuf's dream were marked as "The Alternate State."

The characters' dreams are filled with subtle hints that separate the subconscious from the real world. 

Though a minor detail, Nolan changed the cars' license plates to read "The Alternate State," dropping a hint that the action scene was happening in a dream.

Though Nolan didn't intend to make a movie about a movie, each character represents a role on a film crew.

Nolan didn't intentionally create roles that mirrored jobs on a film set but admitted the filmmaking allegory is "clearly there" during an interview with Wired, 

"I didn't intend to make a film about filmmaking, but it's clear that I gravitated toward the creative process that I know. The way the team works is very analogous to the way the film itself was made. I can't say that was intentional, but it's very clearly there," Nolan said. 

In "Inception," each character can be seen as an abstract version of a movie-making team.

Cobb, who calls the shots and makes the decisions, represents the director. Arthur, who keeps the process moving along and orchestrates all the details, mirrors a producer. Dream architect Ariadne could serve as the set designer, and Eames, who has the power to impersonate others inside of dreams, represents an actor.

As for Fischer, who's having an idea planting in his head, he could represent the film's audience.

"I think that's just the result of me trying to be very tactile and sincere in my portrayal of that creative process," Nolan added. 

DiCaprio helped Nolan make the story more emotional.

Before filming, DiCaprio met with Nolan every day for two months to talk through his character. The relationship proved to be symbiotic.

"I've incorporated a huge number of his ideas," Nolan told The Los Angeles Times of the leading actor.

He added, "Leo's very analytical, particularly from character point of view but also how the entire story is going to function and relate to his character... It's actually been an interesting set of conversations, and I think it's improved the project enormously. I think the emotional life of the character now drives the story more than it did before."

The crew filmed the scene between Stephen Miles and Cobb where Nolan met his wife, Emma Thomas.

According to The Los Angeles Times, the scene between Cobb and Miles was shot at the architecture school at University College London, the university where Nolan studied English and met his wife Emma Thomas. 

The couple has co-produced a number of films including The Dark Knight trilogy, "Inception" (2010), "Interstellar" (2014), and more. 

Brad Pitt and Will Smith turned down the role of Cobb before it was offered to DiCaprio.

Though DiCaprio was the star of "Inception" as Cobb, two other notable actors were offered the part before him, sources told The Hollywood Reporter.

Nolan first approached Pitt for the role but reportedly gave him 48 hours to accept or decline. When he didn't hear back in time, the filmmaker asked Smith to take it on. After the "I Am Legend" actor passed on the opportunity, Nolan asked DiCaprio.

The same four digits appear on the train and taxi in Yusuf's dream.

In Yusuf's (Dileep Rao) dream, a massive train mysteriously appears and plows through the city road.

The train has "3502" written on the front of it. Though the digits are reversed, the same four numbers are seen on the side of a nearby taxi.

While Ariadne tells Cobb that she didn't include the train in her design for the dream, it's not the first time that the topic of trains comes up in the film. 

At the beginning of the movie, Cobb mentions in passing that he "doesn't like trains" when he's with his team.

And several times throughout the film, the line "You're waiting for a train. A train that will take you far away. You know where you hope the train will take you, but you can't know for sure. Yet it doesn't matter" comes up. 

The audience later learns that Cobb and Mal escaped limbo by laying down together on a set of tracks, reciting that line to each other, and getting run over by a train to return to reality. 

The train in Yusuf's dream may serve as a sign that Cobb's projection of Mal is present, trying to influence the events so that Cobb will return to limbo. 

Miles makes a reference to DiCaprio's role in "Catch Me If You Can."

"Extradition between France and the United States is a bureaucratic nightmare," Cobb told Miles as he discusses his plan to return home to his children in the U.S.

The line is a reference to his role as Frank Abagnale Jr., who gets arrested in France and sent back to the U.S. in the 2002 film "Catch Me If You Can."

The code to the safe that Fischer gives to the team, "528491," appears throughout the film.

During Yusuf's dream, Fischer gives Cobb's team the six-digit code "528491" to open the safe with his father's alternate will. Those numbers appear in passing several times after. 

When Fischer is speaking to a blonde woman, who is actually Eames in disguise, during Arthur's dream, she leaves a napkin with the six digits on it.

Also during the hotel dream, the team sleeps in room "528." Arthur also visits the room directly below it, "491," to prepare the charges to wake up the dreamers in the third level. 

Finally, Fischer uses the code "528491" to unlock his father's safe and access his father's will in Eames' dream.

DiCaprio said filming the chase scene in Morocco was the most physically challenging part of the film.

In a scene set in Mombasa, Kenya, Cobb weaves through the packed streets to escape a seemingly multiplying number of men chasing him.

During a Warner Bros. press conference, the lead actor opened up about the intensity behind the scene, which was actually shot in Tangier, Morocco.

"The toughest action sequence, I think that the sequence in Morocco was pretty tough because I had to run through a crowd of people. I felt kind of like a pinball because I was bouncing from Moroccan to Moroccan and falling into various vending machines," he said.

DiCaprio added, "That was a little bit tough but at the end of the day, you'd be surprised. We pulled off a lot of stuff in a day's work that was pretty spectacular."

Nolan wrote "Inception" on spec to control the narrative.

Warner Bros. offered to greenlight "Inception" before Nolan finished the script, but he declined in an effort to maintain creative control.

"I realized with a project like 'Inception' I would be trying to cross certain boundaries of genre and push the envelope of what mainstream movies are allowed to with an audience. I felt it very important that I develop the script on my own. I had to finish it on the page, so at least there would be a specific and clear document in front of the studio of what this film was going to be," he told Deadline.

Nolan explained that he viewed "Inception" as a project he had to tackle on his own, or at least finish the first draft before involving others. 

"The advantage of writing on spec was I got to really thrash out in my own head how to make these things work, and then offer it to the studio for backing and collaboration," he said. 

Warner Bros. and its financing partner Legendary Pictures backed "Inception" with a $160 million budget.

In Greek mythology, Ariadne is a figure associated with labyrinths and mazes.

The figure of Ariadne played an instrumental role in the Greek myth of Theseus and the Minotaur, helping Theseus escape the labyrinth safely.

In "Inception," Ariadne (Page) is an architecture student who designs dreams with layouts that give the dreamers a leg up from the projections.

Both women assumed the responsibility of getting the men around them to safety, using clever strategy and bravery to accomplish their missions. 

When Ariadne proves her ability to Cobb by drawing an unsolvable maze, she forms a circular formation on her third try, finally succeeding. While the page is only shown for a moment, the design resembles King Minos' labyrinth used to withhold the Minotaur. 

The crew used air cannons to cause explosions in Paris.

Chris Corbould, the special effects supervisor, used air cannons to send objects flying through the air in the scene shot in Paris, he told MTV.

After the debris was floating, the team used cameras that catch 1,500 frames each second for the full effect.

"We shot it with super-high-speed Photo-Sonics cameras to get that material floating in the air," he said.

Corbould explained that the team used computer graphics to extend the time the objects floated and dramatize the effect.

Eames' dream was inspired by James Bond films.

Nolan is a huge fan of James Bond films, so it comes as little surprise that he drew on movies like "On Her Majesty's Secret Service" (1969) and "For Your Eyes Only" (1981) to create Eames' dream sequence. 

"We were wondering, 'How are we going to capture that action?'" cinematographer Wally Pfister told MTV. "We went back to watch Bond films."

The team faced a real blizzard while filming in Calgary.

It took two weeks to shoot Eames' dream in Calgary, cinematographer Wally Pfister told MTV. And while they took the time to build a massive set, there was no guarantee that it would snow. 

"We found ourselves praying for snow. It could have gone either way. It was eight months of biting our nails hoping we'd get some snow," he said.

The crew was prepared to make their own snow, which Pfister said wouldn't have achieved the same effect. 

"You've got to be careful what you hope for, because we got a blizzard," he said. "It made shooting difficult and cold and uncomfortable."

Arthur's line telling Saito not to think about elephants is a reference to George Lakoff's book "Don't Think of an Elephant."

When Saito asks about inception, Arthur argues that it's impossible by citing a real-life example.

"I say to you, 'Don't think about elephants.' What are you thinking about?" Arthur asks Saito. 

The businessman responds, "Elephants."

The line is a reference to George Lakoff's 2004 book titled "Don't Think of an Elephant," which examines the way politicians frame key campaign issues to create a certain connotation in voters' minds.

The book's title comes from a study conducted by Lakoff, a linguistics professor, asking his students not to think of an elephant. Though he tries to steer the students' thoughts away from the animals, they're already in the frame and therefore in the students' minds. 

The last line of the movie hints at the opening scene.

When Cobb returns home to see his children, he finds Phillipa and James playing outside with their backs toward him. Viewers see a nearly identical shot in the opening scene, during which the children build a sandcastle on the beach. 

"Look what I've been building," James told Cobb as he greets him in the final scene. "We're building a house on a cliff!"

Though Nolan brushed off the line as an improvisation by the child actor, the mention of a "house on a cliff" does relate to Saito's palace, which sat atop a cliff overlooking the ocean in limbo.

The ending of "Inception" is contested, as viewers never see whether or not Cobb's totem falls down to confirm that he's returned to reality. However, James' line draws a distinct parallel back to Cobb's time in limbo.  

It's also possible that Johnathan Geare, who portrayed James at the end of the movie, unknowingly played into the audience's lingering question, setting up the perfect open ending.