Two decades ago, Terry Gilliam’s 12 Monkeys gave audiences a haunting sneak peek into the first decades of the 21st century—an era in which bears were supposed to roam snowy city streets and the one percent of the human population that managed to survive a dreadful virus has been driven underground. After 20 years, the film’s funhouse-style dystopia still gets audiences shivering, but it has retained much of its mystery, too. In honor of the sci-fi flick’s anniversary, here’s a dossier of 12 Monkeys facts that even the most detail-oriented of time travelers might never have seen coming.

1. IT’S BASED ON THE FRENCH SHORT FILM LA JETÉE.

Chris Marker’s 1962 short La Jetée was the inspiration for the “unusually literate script by David and Janet Peoples” that became 12 Monkeys, according to Turner Classic Movies. The 26-minute piece follows a similar story to the Peoples’ version (with its enslaved, time-traveling protagonist struggling to avert the horrors of a society ravaged by nuclear radiation rather than a viral pandemic), and both films make reference to Alfred Hitchcock’s Vertigo, which influenced Marker’s short film.

2. TERRY GILLIAM HAD NEVER SEEN LA JETÉE.

Unlike his screenwriting team, who took so much inspiration from La Jetée, Gilliam admitted that he hadn’t seen the French short before directing its pseudo-remake. “If I do something based on something else I make it a principle not to read or see the original,” Gilliam explained. “I'll be intimidated by it, or I'll feel an awesome sense of responsibility. So I avoid that problem. When I made Brazil I'd never read [George Orwell's] 1984.

3. THE SET DESIGN CONTAINS NODS TO DECONSTRUCTIVIST ARCHITECTURE. 

Fair use via Lebbeus Woods (cropped)/YouTube

“We were sitting in our first meeting,” explained production designer Jeffrey Beecroft, “and we wanted the sadness of this photographer [Josef] Sudek and the architecture of Lebbeus Woods,” a famously experimental architect and artist. A scene in which protagonist James Cole (Bruce Willis) is half-interviewed, half-interrogated by a spherical robot while strapped into a wall-mounted chair, for example, directly reflects Woods' Neomechanical Tower (Upper) Chamber. “[No] one's ever built anything [Woods has] drawn, because it doesn't stand up. So I built it! And it doesn't make sense, but it works,” said Beecroft.

4. THE FILMMAKERS WERE SUED FOR ONE OF THOSE NODS.

Rather than be flattered by the homage, Woods objected to Gilliam and Beecroft’s unauthorized use of his design in constructing their set, and so he sued the pair, along with the film’s producers and distributors. The matter was finally put to rest years after the film’s release, with Woods receiving a six-figure settlement.

5. BRUCE WILLIS WAS WORRIED HIS TOUGH GUY IMAGE WOULD HOLD HIM BACK.

In 1995, Gilliam told the Associated Press that he first met Willis while considering him for the lead in 1991’s The Fisher King, and that 12 Monkeys was a fresh opportunity for both the director and actor to step out of their cinematic comfort zones. At the time, Gilliam said, "Bruce was concerned whether the baggage he brought to the film was going to be detrimental to it [and] was desperately feeling he wanted to escape the trap of success."

6. WILLIS TOOK A PAY CUT FOR THE GIG, AND EVEN OFFERED TO SHAVE HIS HEAD.

As Den of Geek reported, Willis and his co-star Madeleine Stowe both accepted substantially less than their usual pay rates for their roles in 12 Monkeys in order to work with Gilliam. During the intensive filming process, it was Willis who came up with his character’s signature hairstyle. “It was his idea to shave his head, and it changed him a lot,” Gilliam said. “It makes him much stronger, much more dangerous. He looks like a prisoner from a Soviet Gulag ... Bruce has got one of the great architectural craniums in the world! It's just a great, beautiful thing to photograph.”

7. WILLIS WAS GIVEN A LIST OF ACTING CLICHÉS TO AVOID.

According to BBC, Gilliam gave Willis a personalized list of acting clichés he wasn’t allowed to bring to the 12 Monkeys set.

8. BRAD PITT UNDERWENT PSYCHIATRIC COACHING FOR THE ROLE.

Dr. Laszlo Gyulai, who directs the University of Pennsylvania School of Medicine’s bipolar disorders unit, helped the then-up-and-coming actor to fine-tune his institutionalized character’s mannerisms through the study of real mental illness. Gyulai told The New York Times that films featuring psychiatric patients sometimes “make them look like lunatics, [while] many patients who are mentally ill are not crazy at all, particularly if they have depression or mood disorders.” Legend has it that Gilliam put an extra and very genuine bit of tension into Pitt’s performance by taking away his cigarettes on set, too.

9. PITT'S HARD WORK EARNED HIM A GOLDEN GLOBE, AND HIS FIRST OSCAR NOMINATION.

12 Monkeys made its splash at the box office just as Pitt’s career was hitting overdrive, and his Academy Award nomination and Golden Globe win for Best Supporting Actor were among the actor’s very first accolades. As the Manila Standard reported, Pitt was “surprised” by his 1996 award, and kept his comments brief during the “moment of absolute terror” in which he delivered his acceptance speech, stating: “I'd like to thank the members of—actually, the makers of Kaopectate. They've done a great service for their fellow man.”

10. THE FILM’S EERIE MAIN THEME IS INSPIRED BY ARGENTINE TANGO. 

In a 1996 interview, Gilliam explained to film critic and Monty Python-expert David Morgan that the work of Argentine tango composer Astor Piazzolla and other tango stars served as the basis for 12 Monkeys’ jaunty-yet-creepy main musical theme:

“I grabbed some other CDs including this guy Piazzolla, whom I had never heard of. And a couple of the pieces just stuck with me, and I was convinced they were right for the film and I wanted to use them … And then, I don't know, it just hit me—it's the 12 Monkeys theme! It's Jeffrey's theme, or the monkeys' theme.”

11. GILLIAM’S OBSESSIVE “HAMSTER FACTOR” SLOWED SOME THINGS DOWN.

The term was coined by the 12 Monkeys production for identifying “those moments during shooting when Gilliam became obsessed with small details at the expense of the bigger picture,” explained Variety. The word on the bear-filled street is that it specifically came about after the director insisted on spending the better part of a day waiting for a hamster that appeared in the background of a shot with Bruce Willis to get with the program and run in its wheel.

12. FOR GILLIAM, MAKING THIS MIND-BENDING MOVIE “WAS EASY.”

 “It was easy,” Gilliam told Den of Geek of the production. “Because [producer Chuck Roven] came to me with a script ... and the studio spent $1 million on the script alone. They wanted to get their money back.” With the film’s complex script already sorted out, Gilliam said, his main task was “basically to find a cast to make it work.”

Once Willis had been cast, Gilliam explained, “we were off running, and Brad [Pitt] was the icing on the cake. And then we made the film.” And despite iffy feedback from test audiences, the film raked in over $168 million internationally—more than quintupling its $29.5 million budget.

“It was just all these coincidences leading to the success of it [but] it proved that there was an audience for intelligent films,” said Gilliam. “But immediately after it became a big success, I had a meeting with the studio, and their reductionist theory of its success was very simple. Two words: Brad Pitt."