On June 15, all four seasons of 12 Monkeys—the epic Syfy series that sent characters James Cole (Aaron Stanford), Dr. Cassandra Railly (Amanda Schull), Jennifer Goines (Emily Hampshire), José Ramse (Kirk Acevedo), Teddy Deacon (Todd Stashwick), and Dr. Katarina Jones (Barbara Sukowa) through basically every era of time you can imagine as they tried to save the world from the Army of the 12 Monkeys—will be available for streaming on Hulu. Mental Floss chatted with co-creator and showrunner Terry Matalas and stars Schull and Hampshire to bring you fun facts and behind-the-scenes stories about the show. Beware: Spoilers for the series ahead!

1. The show that would become 12 Monkeys didn't originally have anything to do with the film.

The TV version of 12 Monkeys began as a writing exercise for co-creator and showrunner Terry Matalas. “I’d always wanted to do a serialized time travel show,” he tells Mental Floss. “So I sat down at my kitchen table and started writing this thing called Splinter.” After penning the first three acts, he handed the script off to his writing partner (and eventual co-creator) Travis Fickett, who wrote the back part of what would become Splinter's pilot episode. The reactions to the sample were enthusiastic, and eventually, it ended up in the offices of Atlas, the production company that made Terry Gilliam's film version of 12 Monkeys.

Atlas told Matalas and Fickett they’d been trying to turn the movie into a show for years and thought they could do it by reworking the Splinter spec script. Matalas suggested that, rather than rewriting the pilot entirely, they change some of the characters’ names—“it was always about a woman named Cassie who was a virologist, but his name wasn’t Cole, I think it was Max,” he says—and mention the Army of the 12 Monkeys at the very end of the episode, then go from there. “That just seemed like a really exciting way to reboot,” Matalas says. “Having the intellectual property gave us an opportunity to expand that world [from the film], but at the same time, we could write it in the tone of what Splinter was. And so the rest is history.”

2. 12 Monkeys took some inspiration from HBO’s True Detective.

Gavin Bond/Syfy

In addition to the characters’ names, fans of the 12 Monkeys movie will find little nods to the film in the show—Jennifer Goines wears a yellow sweatshirt, as Brad Pitt does in the film, for example, and the hospital J.D. Peoples is named after the film's screenwriters (Janet and David Peoples)—as well as to the short film the movie was based on, Chris Marker's La Jetée. But there are influences beyond those sources, including the first season of HBO’s True Detective.

“Some of the weirdness of True Detective found its way into the Army of the 12 Monkeys,” Matalas says. “I always felt that, even though it was a science fiction time travel show, there was also a supernatural/horror aspect to it—that the Army of the 12 Monkeys needed to be weird, mysterious, and scary, and have a sort of visceral apocalypse that they wanted to bring about.”

3. The co-creators of 12 Monkeys researched real theories of time travel for the show.

Matalas and Fickett made a number of changes to adapt 12 Monkeys for television. They began with the fact that in the film, time is a closed loop—its characters can’t make any changes to the past. “That just doesn’t seem like a great goal for a long series,” Matalas says. “To never see a change made in causality is a missed opportunity for the longer narrative.” Though Matalas and Fickett looked into actual scientific theories about time travel—they used an Einstein-Rosen bridge as one of the inspirations for how the machine sends people through time, for example—they didn’t necessarily apply all of that information. “You get into quantum theory and quantum universes and then you can lose yourself real quick,” Matalas says.

The duo leaned into the idea of paradoxes—that an object coming into contact with a version of itself from another time would create an explosion—and built a grand mythology for the show, including the Red Forest, the Messengers, Titan, the Witness, and, of course, Primaries: the humans who are entwined with the very fabric of time. If enough of them are paradoxed, they could destroy time—which is the ultimate goal of the Army of the 12 Monkeys.

“There’s the easy sci-fi version of this: The Army of the 12 Monkeys goes back in time and sets off ‘time bombs,’ and we have to stop the time bombs from going off,” Matalas says. “It just seemed kind of hokey.” But they had a breakthrough in the writers’ room when they started talking about the evolution of man—and of time, which, of all the species on earth, only man seems to be aware of. “Even though time is this force of nature, the introduction of man could have changed its evolution. Could we have evolved with it in some way?” Matalas says. “So we created a network of people—Primaries—that were a part of time because of this evolution, and it suddenly became personal, so it felt right.”

4. 12 Monkeys star Aaron Stanford auditioned to play Ramse before he landed the role of Cole.

Kurt Iswarlenko/Syfy

Stanford—who Matalas had worked with on Nikita—sent in a taped audition for the role of James Cole, but it got lost. So when he came in to audition, he read for José Ramse, Cole’s best friend. “We were at a situation where we really needed to find our two leads, so we did a chemistry test with him and Amanda [Schull],” Matalas says. “The second the two of them walked in together, [we] just knew.”

When auditioning actors for the role of Deacon—who is at first the leader of the post-apocalyptic gang the West VII before eventually becoming a traveler himself, and was described in the casting call as "a young Ed Harris type"—“we saw every young Ed Harris type there was in Los Angeles and New York,” Matalas says. “And then in came Todd ... and he was like, ‘F**k this. I’m not going to be that guy. I’m going to be this guy who’s really charming.’ And it was like, ‘It’s him.’”

Matalas says they got exactly who they wanted for their entire cast. “Barbara [Sukowa] for [scientist Katarina Jones] was the only Jones. We read some really great people, well known people, but there was just something perfect about it—and she did it on her iPhone,” Matalas says. “Same thing with Jennifer Goines. We saw a lot of people, but the only one I ever sparked to was Emily Hampshire.”

Throughout the whole series, Matalas only wrote two characters for the actors who ended up playing them. “The first was Hannah Waddingham, who played Magdalena,” Matalas says. “I think we said ‘Hannah Waddingham type from Game of Thrones’ [in the casting call], and then we got her. And then the only one I ever considered for Athan was [Battlestar Galactica's] James Callis.”

5. After landing the role of Jennifer Goines in 12 Monkeys, Emily Hampshire spoke with a psychologist.

Gavin Bond/Syfy

On the advice of a director she knew, Hampshire didn’t watch the movie version of 12 Monkeys before she auditioned for the role of Jennifer Goines. It turned out to be the right move: “Terry [told me], ‘We cast you because you didn’t do an impression of Brad Pitt. You did your own thing,’” Hampshire tells Mental Floss. “I felt like I really connected with the Jennifer that was on the page—like I totally understood this logic. It actually felt easy for me, which nothing ever does.”

After she was cast, the show brought on a psychologist to make sure Jennifer’s dialogue was authentic and to discuss the role with Hampshire. “He said that a lot of people with mental illness don’t have that filter that we have in society—they just say the truth, like children,” Hampshire says. “That’s kind of what I always felt with Jennifer—that she was a truth teller. Whether you think this is mental illness or not, it is, to her, just the truth. So that’s mainly what I got from it.”

6. Amanda Schull researched virology after she was cast as Dr. Cassandra Railly in 12 Monkeys.

Kurt Iswarlenko/Syfy

Like Hampshire, Schull didn’t watch the movie before she auditioned. “I had seen the movie years prior and then I didn’t watch it again before I got the role because I didn’t want [Madeleine Stowe’s] performance to influence me,” she says. But once she booked the role, Schull rewatched the movie—and did a lot of research into virology. “I studied journalism in college, so I like to have all of the information, even if it doesn’t necessarily have an effect on the superficial,” she says.

For episode three, where Cassie is in Haiti fighting a virus outbreak, “I was researching all these different viruses and the side effects and what would happen and how we should take off the gloves—which was helpful—but the other things weren’t really going to have any effect on performance or the dialogue. Maybe it’s good to know, but then we sort of veer off into this total fictitious world with a fictitious virus that is very different from any other virus. So I tried, and then I realized that I needed to pave my own way.”

7. Hampshire's most challenging day on 12 Monkeys was her first one.

The first day on a new set can be nerve-wracking for any actor. Typically, Hampshire says, productions will schedule easy things—“stuff like walking across the street”—on that day to help the actors get comfortable. Not so on 12 Monkeys; on Hampshire’s first day, she had to film complicated dialogue and threaten a tied-down Stanford with a scalpel for the episode “Mentally Divergent.”

Hampshire had never worked on an hour-long drama before. “I was used to doing these little indie movies, and this was the fastest pace I’d ever been on,” she says. “To me, everything about Jennifer was how I moved. [The director] wanted me to do a walk and talk with Cole—you start the thing here and you end up here. I f**king couldn’t get out all my dialogue in that time. I was just trying everything not to cry and I ultimately did end up crying but trying not to show I was crying.”

Eventually, Matalas took her aside and encouraged her to do things her way. “It was a horrific day but also a big learning curve for me,” she says. “I learned everything in that day of doing the TV show like that.”

8. 12 Monkeys' time travel chair was, in Schull's words, a “death trap.”

Ben Mark Holzberg/Syfy

Most of the main cast members of 12 Monkeys, at one point or another, have had to run up a set of stairs and fling themselves into the time travel chair in order to splinter. It was, according to Schull, a precarious affair: “Every single one of those stairs had a teeny tiny little lip that was imperceptible to the naked eye but very capable of catching your foot going up or down,” she says. “The stairs were all graded and so when Cassie was running up or down in heels in an urgent way—as one does coming to or from a disaster where time travel is necessary—my heels would always get caught. Also, the railing going down the side was a chain, so you’d go to grab it to steady yourself and you’d go flying off the side. I caught my calf and the edge of my pants and shin bone every single time I got in or out of that chair with urgency.”

The chair itself was no picnic, either. “When you got into it for the first time, you’d go flying backwards—you wouldn’t realize that it was going to stop,” Schull says. “There are tufts of my hair forever stuck in the headrest of that chair. It was a death trap.”

9. 12 Monkeys' costume department faced a number of challenges.

BEN MARK HOLZBERG/SYFY

“Like the people on our show, we’re always battling time,” costume designer Joyce Schure told Mental Floss when we visited the set last year. Depending on the era, the department had to go shopping for pieces (often at thrift stores) or source outfits from costume houses. But for the leads, they’d often have to design and make multiple versions of elaborate costumes not just for the actors, but for stunt and photo doubles, too. Shooting outside meant having to line the costumes with felt or fleece so the actors would stay warm. And, of course, they needed to be able to move. “Cassie’s dresses needed to be beautiful but she also needed to be able to high tail it after a bad guy—and that goes for the shoes as well,” Schull says. “Every single fancy ball gown was met with a series of challenges.”

Even though there was a constant time crunch, the department never skimped on the details. One of Schull’s 1940s costumes from the fourth season had a low-V back with “this beautiful body chain across the back and then a single pearl dangling down,” Schull says. “When I ran or I moved, the dress fanned open with gold and cream art deco paneling in the front. It’s really, really intricate and beautiful.”

In a post-apocalyptic world, no clothing could ever look brand new—so clothes that were supposed to be from 2043 went to the breakdown department, which used techniques from putting kidney beans in the pockets of clothes and sanding them to create texture to washing leather to age garments. For most of the series, they did each piece by hand, but while filming the fourth season, the department discovered a time-saving breakdown technique when they had to age a lot of clothes quickly: “We found out you can get a cement mixer, fill it with rocks, and throw all that in, and it will beat up everything,” Schure said.

Each character has an established costume look, and there will be nods to that style in all of the costumes, no matter what time the character is in. “For example, in Jennifer’s case, she’s always a double sock girl—she always wears tights with double socks,” Schure said. Sometimes the actors even got to weigh in on their looks: Hampshire collaborated with Schure on her 1920s costumes, one of which was inspired by the poster for Charlie Chaplin’s The Kid.

10. Hampshire filmed one 12 Monkeys scene with a rat—and it pooped in her mouth.

Initially, the production team wanted to use a spider for a season one scene where Jennifer is being tortured by the Army of the 12 Monkeys—but Hampshire is terrified of spiders, and Jennifer, in her own way, had to be having fun. So when the assistant directors emailed her asking how she felt about spiders, Hampshire responded, “‘I feel like this is never going to happen. No. I’m also deathly allergic!’ Which I wasn’t, but whatever.” They offered her a scorpion and a rat, and she agreed to both: “I was totally cool with everything but spiders, just to make sure that I wouldn’t get spiders!”

Hampshire had a meet-and-greet with the whip-tail scorpion—which she says is “basically the most spider-looking scorpion of all scorpions”—in an office conference room, and though they filmed a scene with it (which you can see here), they instead ended up using footage of the rat … which, Hampshire notes, pooped in her mouth as they were rehearsing the scene. “The wrangler was like, ‘This was his first thing ever and he was nervous,” she says. “I just spit it out. I feel like I had to go into this other kind of zone [for that scene].”

It wasn’t the last time an animal she was working with pooped in her presence: Terry the tortoise, Jennifer's pet in 2043, “sh*t the bed in his first scene,” Hampshire says. “They had to change all the sheets in Jennifer’s tent!”

11. Schull learned how to ride a horse to go to the Wild West on 12 Monkeys.

The fourth and final season of 12 Monkeys sends Cassie, Cole, and company back to the Wild West—which meant that the actors had to saddle up. Schull trained on one horse but had a different one the day of shooting. “My horse was really not into me,” Schull says. “It’s easy to look tense and horrible on a horse, so I was trying to look as cool as I possibly could and my horse was doing everything he could to totally bomb that for me.”

Schull tried to get on his good side by slipping him some snacks (with permission from one of his handlers), but all that did was make the horse hungrier. “There’s a scene that we shot immediately following that interaction,” Schull says. “I think Aaron and I are sharing a thermos of water and discussing what we need to do, and the horse was in the background—he was supposed to just be still, but he became ravenous because I’d broken the seal and given him carrots and celery. He was eating a tree in the background and nobody could stop him.”

As the day went on, the horse got tired, and therefore easier to control, but it was still a stressful situation: “If we had had all the time in the world it probably wouldn’t have been so stressful, but when you’re light dependent and there are so many scenes that you have to get done, it is stressful,” Schull says. “You just want to try to be the cowboy that you’re there to be, but it doesn’t always work that way with animals.”

12. There were lots of on-set pranks and giggle fits on 12 Monkeys.

Monkeys is a serious show, but the cast and crew had plenty of fun in the breaks between shooting on long days. “The lighting setups were really long—longer than any show I’ve ever done because the lighting is almost another character,” Schull says. “Nobody ever left to go be on their own in their own trailer. Everyone stayed and talked.” They’d also do silly dances and singing; sometimes they made up their own games to pass the time. And sometimes, they’d play pranks on each other.

Schull once swiped Hampshire’s stuffed animal and snapped pictures of it—with Hampshire’s phone, which she also snagged—on adventures around the set. Hampshire says that Matalas would put his gum wrappers and pistachios shells in her shoes and purse: “There’s not a day that I didn’t go to put on my shoes where there wasn’t garbage in them. That stuff keeps you going.”

Generally, Schull says, the cast really kept it together, even when they were getting loopy from shooting for so long. But not always. Once, when Cassie was supposed to be performing an operation, Schull realized she didn’t have enough surgical props to make it look like she knew what she was doing. Sukowa and Hampshire started to make fun of her—"Barbara said it looked like I was digging a hole in [the patient's] stomach"—and before long, they were all laughing too hard to continue. “Production had to come to a halt—we had tears streaming down our faces," Schull says. "Makeup had to be called in to wipe it all up.”

Another time, when they were shooting a key season three sequence at 4 a.m., Schull cracked “a really vulgar joke” that set Sukowa off. “Barbara’s laugh is so contagious," Schull says. "The two of us started to laugh so hard and every once in a while after that she would look at me, repeat the joke, and just start laughing.”

13. Orphan Black’s Tatiana Maslany gave Hampshire advice for how to play opposite herself on 12 Monkeys.

Throughout the show, Hampshire plays Jennifer in both 2016 and 2043, and turning her into old Jennifer took as long as five hours. “You could never pay me enough to be a Klingon,” Hampshire says, because the prosthetics—which were glued to her face—“were so itchy and uncomfortable, and then taking them off is hard. But for the experience of being Old Jennifer, it was definitely worth it.”

For scenes where young Jennifer had to interact with old Jennifer, Hampshire got some advice from Tatiana Maslany, who won an Emmy (and scored a Golden Globe nomination) for regularly playing multiple versions of herself on Orphan Black. “The best advice she gave me was to do the character that is driving the scene first,” Hampshire says. “Once the pace of the scene is set, it’s done—you have to match that. So make sure you try out one side and do the next and then start with the character that’s driving the scene.”

14. The chase through time in season 3 of 12 Monkeys was done in eight hours.

In one incredibly cool season three sequence, Cassie and Cole chase their son, Athan, down the same street over three different time periods. At first, pulling off the sequence seemed impossible, both from a time and a budgetary standpoint. But the cast and crew did it in one eight-hour shoot. “We write with our production team so that we can absolutely stretch the boundaries of what our coin allows us to do,” Matalas says. “In this case, we had to dress [the area] in three different time periods, but we kept progressing the street forward—so you didn’t have to redress as much of it as you would think. And then we just shot at different times of night. It’s all about producing smart.”

15. One cut set piece from season 4 of 12 Monkeys would have sent Cassie to space.

Yes, you read that right. “It involved splintering Cassie for 45 seconds to a post-apocalyptic International Space Station to get some data off the hard drive,” Matalas says. “It was really cool, and it made sense, and it would have been scary, knowing people had died up there and it had been decades.” Ultimately, time constraints meant the sequence had to get the axe: “I think if we had two more episodes [in Season Four] we could have pulled it off.”

16. There were, on average, 60 to 75 visual effects shots in each episode of 12 Monkeys.

“Some episodes are as high as 100 to 125 shots, while others can include as little as 30,” Sébastien Bergeron, founder and VFX supervisor at Folks VFX, wrote in 2017. “The bulk of the work is creating unseen environments, but there’s a variety of other work, too: environment work, big futuristic cities, a time-traveling city, twinning of characters when they meet themselves in the past, destruction, explosions, all sorts of FX and particles—pretty much everything.”

One shot from the season three premiere required Folks to create a post-apocalyptic Times Square. “We did a crane shot in a field with a blue screen where James Cole steps onto a rusty, old bus on his side to finally discover an overgrown Times Square,” Bergeron wrote. “This one was particularly challenging as everything in there was CG.”

17. The different time periods on 12 Monkeys are shot differently.

“With multiple time periods, you get to change the look of your show entirely,” Matalas says. “The ‘70s can feel like a Polaroid. And then you’re going to a rich, saturated 1940s”—his personal favorite time to visit. “It’s pretty cool.” The show has been nominated for multiple cinematography awards, both in the U.S. and Canada; Boris Mojsovski, who came on board during the show’s second season, won an American Society of Cinematographers Award for the season three episode “Thief.”

18. Hampshire and composer Stephen Barton wrote a song for the final season of 12 Monkeys—and recorded it at Abbey Road.

In the second episode of Season Three, Jennifer Goines (as J.H. Bond) puts out a song called “Jones, Pourquoi C’est Si Long?” (or: “Jones, What’s Taking So Long?”). Hampshire improvised a bit of the song, which made it into the episode—and became an on-set earworm. “Everybody started singing it,” Hampshire says, “so then Terry was like, ‘I think we’re going to have to write Jennifer a song.” Hampshire penned the lyrics (in French) and Barton wrote the music for the song, which was recorded at Abbey Road with period instruments. The song was featured in the episode “Die Glocke,” which also saw Jennifer serenading a certain fürher with Pink’s epic kiss-off anthem “U + UR Hand.”

Some other songs were suggested for the scene, including one from The Sound of Music. But “U+ Ur Hand” is one of Matalas’s favorite songs. “I was shy to pitch it because it was going to betray my workout music,” he says, laughing. “I just happened to really love that song. It’s just a propulsive anthem—it’s perfect.”

19. Matalas’s favorite scene to film was in the second episode of Season 4, “Ouroboros.”

Matalas says that "Ouroboros" was a love letter to 12 Monkeys. “My favorite scene to film was when Jones and Cole watched the first splinter in 402,” he says. “[It's] one of those rare things you can only do in a time travel show, where you have these seasoned travelers now, who have been through so much, bruised and battered, emotionally destroyed, watching their younger selves set out on this journey, as they themselves are about the approach the end. It was powerful to shoot, powerful to score, it still remains one of my favorite scenes in the series.”

The most challenging episode to film was Monkeys’ two-part finale. “The finale was just so big, and I was directing it,” Matalas says. “Particularly the battle in Titan with Cole and Ramse and Deacon running around taking out the Army of the 12 Monkeys. We shot it at an actual oil plant that was shut down in Sarnia [a city in Ontario, Canada], which looks like a giant time machine. But we only has eight hours of night to do it. My DP, Boris, and I were just running around guerilla style trying to get it all—and we did. But I wasn’t entirely sure it was all going to work until deep into editing it and cutting it that we realized we got enough to make it work. So it was nerve-wracking to say the least.”

20. In the 12 Monkeys series finale, Cole and Ramse were going to take on the Army of the 12 Monkeys to a Journey song.

One scene in the show's final episode features Cole and Ramse in a car, racing toward the Army of the 12 Monkeys with Bill Medley and Jennifer Warnes's "(I've Had) The Time of My Life" playing on the radio. The song was perfect for the scene—but it wasn't Matalas's original choice. “It was originally going to be Journey’s ‘Don’t Stop Believin’,’ and Journey said no,” Matalas says. They started searching around for something else when “(I’ve Had) The Time of My Life” popped up on Matalas’s playlist in the car. He had his editors put the song in an early cut to see how it would play—and it was perfect. He thought approval was a long shot, but it came through. “It could not have been more perfect,” Matalas says. “Actually, I‘m very grateful that Journey said no, because this was infinitely better.”

21. 12 Monkeys was laden with easter eggs hinting at future plot developments.

“There’s so many,” Matalas says. The fact that Hannah was Cole’s mother, which was revealed in the fourth season, was something Matalas had told Brooke Williams on her first day of shooting. “She always knew, and would adopt little mannerisms,” he says. But once they knew the end was coming, they began giving little hints. “It’s the reason that [the first episode of season 3] starts with a Hannah-Cole team up. They’re very similar,” he says. “Jones calls [Hannah] a little sh*t, Hannah calls [Cole] a little sh*t, Cole calls Athan a little sh*t. It’s sort of this generational thing, apparently, a lovely insult that they pass on to each other. I thought it was kind of obvious, because it was such a strange little turn of phrase for someone to be saying on the show, but yeah, it was all right there.” Pay close attention to Athan’s visions in Season 3, meanwhile, and you’ll see glimpses of Titan destroying the world—a nod to the events in the finale.

22. After filming on 12 Monkeys wrapped in Toronto, the evidence board made Matalas emotional.

After 12 Monkeys wrapped in Toronto, the cast and crew still had scenes to shoot in Prague. But, says Matalas, “it really felt like the show ended on those soundstages. I remember walking through after we wrapped with Amanda, each of us kind of saying goodbye to these sets that we’d been on for four or five years. And I remember thinking that when I saw the time machine for the last time, that would really be where the tears would come. But it was actually the evidence board, because the evidence board had four seasons of stories up on it. It was all this history. And that made me… That really, really got me.”

23. Schull and Hampshire took home a number of props and costumes from the 12 Monkeys set.

Schull has all of Cassie’s coats—“I don’t think her coats got nearly enough recognition; the downside is that I live in Los Angeles where I get to wear none of these things”—and a Raritan National Laboratory plaque that she took from set. “But the thing that was given to me that means the most is Cassie’s watch with the original scratch,” Schull says.

Hampshire has a number of Jennifer’s costumes as well as the E.T. and chestburster alien from Jennifer’s star turn as J.H. Bond in 1920s Paris. But her favorite item isn’t a prop: It’s a sock monkey made for her by the costume department, a nod to Jennifer’s double-sock costume motif. “Inside it’s stuffed with pieces of all her costumes,” Hampshire says, "with fur ears and buttons that came from her costumes.”

24. Matalas took home 12 Monkeys’ time machine—and one other, creepier prop.

Though the time machine itself is gone, Matalas has the most important part of it: The chair is stashed in his garage, right next to the Delorean from Back to the Future that Matalas restored. Also in the garage? The corpse where the virus originated (a.k.a. the splintered-in-half body of Olivia, the Witness). “I still have that body in my garage, and I don’t know what to do with it,” he says. “It’s in a Tupperware™ case and I opened it up the other day and was like ‘Oh god!’” He knew in Season 1, he says, that the body that held the virus wouldn't be Cole, but would be the Witness.

25. Matalas always knew what the last scene of 12 Monkeys would be—but not necessarily all the details of how they'd get there.

Ben Mark Holzberg/Syfy

“I would say, in the first half of season one, we knew the whole season one arc, but we didn’t really know the whole entire series,” Matalas says. “It wasn’t really until season two—when Cassie was pregnant and we knew we were at the midpoint—that the rest of it played out. At that point we had to figure out the rest because we would get caught with our pants down if we didn’t. I knew enough to know, yes, Cassie is pregnant, but is the kid the Witness? I knew that couldn’t necessarily work, that there had to be some other element to it.” He loved the idea of having Olivia (Alisen Down), the leader of the Army of the 12 Monkeys, go from “hating the Witness, only to discover that she is the Witness,” he says.

Once season two was finished, Matalas and the writers pulled out the white boards to map out the rest of the show—and the last scene was exactly what Matalas had envisioned all along: Cole and Cassie reuniting. “The ending was always that: You would think Cole was erased, but at the last moment, he would come back to her. The surprise ending of 12 Monkeys would be the fact that it was a happy ending, and that you’d be fully satisfied,” he says.

26. In Matalas’s view, Cassie and Cole are not in the red forest.

The final shot of 12 Monkeys features a red leaf—not unlike one that would be seen in the Army of the 12 Monkeys’ timeless Red Forest. “The red leaf was designed mostly because the show suggests it wouldn’t have a happy ending,” Matalas says. “So that if that’s the ending that you prefer—that there was a darker, more insidious, more twisty choice—you could make it. You could look at the finale and argue that Cassie never turned off the machine in Titan.”

That’s not Matalas’s interpretation of the ending, though. “I think it’s pretty clear that they saved the world, and it’s just fall, and that the red leaf is just the symbol of the show,” he says. “But … there are people, even some on our staff, who believe that they’re in the Red Forest. Which I don’t think holds water. I don’t know why in the Red Forest Cole needs to go kill himself and Jones needs to die. That seems weird to me. But you can go there if you like!” As Jennifer Goines once said, the right ending is the one that you choose.

This piece was updated in 2019.