Well, here's a twist: The Sixth Sense came out 25 years ago.

Countless imitators later, the M. Night Shyamalan-directed thriller starring Haley Joel Osment and Bruce Willis remains the gold standard when it comes to jaw-dropping endings (spoilers ahead, but, to be fair, you've had a quarter of a century to catch up). Though even once you know, the actors' pitch-perfect performances and the unsettling vibe that permeates the entire film have made the 1999 blockbuster an enduring rewatch.

"There was something magical about his audition," Shyamalan said in 2019 of Osment, who wasn't a newcomer but gave a zero-to-100 breakout performance as dead-people-seeing Cole Sears. As he recalled to The Hollywood Reporter, "When I left the room I told the casting director, 'I don’t know if I want to make the movie if it’s not with that kid."

The Sixth Sense turned Osment into the child star at the age of 10, and it became the top-grossing movie of Willis' stacked career. (In fact, the film's $294 million haul in the U.S. and $673 million global box office was topped only by Star Wars: Episode 1—The Phantom Menace that year.)

Also critically acclaimed, it was nominated for six Oscars, including Best Picture, Best Actor for Osment, Best Supporting Actress for Toni Collette for her turn as Cole's understandably concerned mom Lynn, and Best Director and Original Screenplay for Shyamalan.

The filmmaker—whose cat-and-mouse thriller Trap, starring Josh Hartnett, is in theaters now—shot The Sixth Sense's scenes in order, which turned out to be helpful for Osment when it came to bringing Cole's haunting journey to life.

"When you have actual memories of going through earlier scenes in the story," Osment explained to THR, "it really helps build the reality of the world over the course of the film."

And his classic utterance of "I see dead people" was just another line when he said it during filming.

"Even when we were shooting that scene, nobody was pointing to that line or singling it out for special attention," the actor, now 36, said. "I don’t even think it really gathered momentum until the film had been out for a while and the advertising started pivoting to including it on the posters and commercials and the like."

It only went on to become one of the most famous movie quotes of all time. And keep reading for more secrets about The Sixth Sense that, much like the film's famous twist, you won't be able to unsee:

1. When M. Night Shyamalan's script began making the rounds, it came with a few stipulations: "I have to be attached as director, and we're going to have [a] $1 million minimum bid," he told The Hollywood Reporter of his demands. "If they want to read it, they have to know that this is going to start at $1 million."

When then-president of production of The Walt Disney Studios David Vogel read the script, he bought the rights to for $2.25 million without corporate approval to avoid a bidding war. Disney did not respond so favorably to his rogue decision-making. They asked him to restructure his contract and give up some of his presidential power. He refused and was fired in July of 1999.

Disney had so little faith in the film that they sold production rights to Spyglass Entertainment, while retaining distribution rights and only 12.5 percent of the movie's box office receipts.

2. A few years prior to playing Malcolm Crowe, Bruce Willis was attached to both star in and produce another Disney film, Broadway Baller. Only 20 days into the ill-fated production, he fired the director and much of the crew, leaving the production to be shelved indefinitely.

Facing a lawsuit and a bill for the $17.5 million already spent on the scrapped film, Willis signed a three-picture contract with the studio in which a portion of his salary would go back to cover the losses. The first was Armageddon, followed by The Sixth Sense and The Kid. 

3. Michael Cera revealed that he'd auditioned for the role of Cole, telling Esquire in 2009 that he didn't know the movie "was about seeing dead people. They didn't mention that in the breakdown."

After seeing the movie, he thought back to the scene he'd read for his audition. "Bruce Willis is saying, 'I can't be your doctor anymore,' and Haley Joel Osment starts crying and slides the penny over to him. It's a very emotional scene. And I did not do it that way," the Arrested Development star recalled. "I did it upbeat. I said 'Some magic's real' very optimistically."

4. Though he's only in the film for about 10 minutes, Donnie Wahlberg underwent a massive transformation to play Malcolm's tortured former patient Vincent, losing 43 pounds in just five weeks. 

"I remember Night saying, 'This scene really has to kickstart the movie,'" the New Kids on the Block singer told THR. "I tried not to think about that burden and that responsibility and just try to honor the script and stay in tune with what I needed to play this part. I thought if I was in that room standing across from Bruce Willis and Olivia Williams and haven't suffered and really gone through some really dramatic situations before I do this scene, how am I going to bare my clothes, never mind bare my soul? So that's just where I went." 

As he explained, he went rather method to prepare for the production, moving to New York and staying in a friend's apartment, "but with no money, no credit cards. I would fast for a couple of days at a time and then just eat vegetables, chew gum all day and then walk the streets. When I got to Philadelphia, I slept in the park one night and was going through this really crazy process."

He couldn't, however, go the full monty for his big moment, as he'd hoped, having to settle for appearing in his "tighty-whities" to ensure the film was rated PG-13.

5. Despite casting himself as Dr. Hill as a "nice little thing" done to acknowledge his parents, both of whom are doctors, Shymalan would end up leaving much of his on-screen performance in his own film on the cutting room floor, declaring himself unhappy with his own acting.

However, he gave himself another chance and has since popped up, Hitchcock-style, in all of his own films.

6. To keep viewers in the dark about Malcolm's fate, a left-handed Willis learned how to write and draw with his right hand so that viewers wouldn't notice that his wedding band was no longer on his left hand. 

7. While Willis went to great care with his handwriting skills to keep viewers on their toes, his wardrobe was one of the few clues apparent throughout the entire film that everything is not what it seems with Malcolm. If you pay close enough attention, you'll see that he's always wearing a slightly modified version of the same outfit he was wearing the fateful night Vincent took his life.

8. Another clue that Malcolm is dead?

After Cole iconically says, "I see dead people," the camera slowly zoomed in on his face.

Producer Frank Marshall admitted in a special feature that he wanted the scene altered, fearing it was too much of a hint, but test screen audiences didn't notice what was being implied, so it was left intact.

9. The color red is intentionally absent from much of the film, though it is used prominently in a few isolated shots for, Shyamalan said, "anything in the real world that has been tainted by the other world" and "to connote really explosively emotional moments in situations."

10. While great care went into protecting the major twist ending, less care was taken when it came to the soundtrack's track listing.

The final track of the James Newton Howard score was originally called "Malcolm is Dead."

While the soundtrack wasn't available until a few weeks after the film's release, it still would have spoiled the film for anyone who happened to check out the CD in a record store (remember those?) before getting to the theater to see it.

11. While Willis may have been obligated to make The Sixth Sense, he was apparently determined to make sure production was a good time for all involved, going so far as to deejay parties for the adult members of the crew at night.

"Bruce definitely introduced me to the notion of partying and letting loose. Back in those days, he was a big DJ and the parties were super fun," Shyamalan told Variety. "He definitely gave me my first hangover. He'd always keep giving me shots that he kept calling 'candy': 'Here's candy, here's candy.' And then the next morning I could not get off the sofa. And I didn't know what this throbbing pain in my head was. He was just laughing his butt off."

12. While much of the terror of the film lies in what you don't see, Osment revealed in a Reddit AMA years later that there was one scene left on the cutting-room floor that might've pushed the movie over the line.

"There is a deleted scene from The Sixth Sense where I look out the window of the hospital and see an entire wing with horribly disfigured and mutilated people standing in each of the dozens of windows," he wrote. "I think Night wisely cut that out because we end up having a movie that isn't too gory and your imagination (the most terrifying force at work) takes over."

13. In the two decades since the film was released, much of the cast has admitted that it wasn't until they saw the thing that they realized how scary it was.

For Mischa Barton, seen in the pivotal role of a young girl who'd been poisoned by her mother, that moment came when she stepped into the ADR booth during post-production.

"I actually had my little sister in the room because we went into this studio in New York to do the ADR and she just, like, literally flipped," the future star of The O.C. told Variety. "You know how you're not supposed to make any noise in ADR? She screamed at the top of her lungs. My mom was like, 'Oh, my God.' She had to take her outside. My sister's like, 'That's the scariest thing I've seen.'"

14. Cole's visible breath whenever a ghost was near? That was achieved the old-fashioned way: By making the actor as cold as possible.

"What they did was they would drape this huge plastic sheeting over the sets and then pump in freezing cold air so that it would be below freezing, and you could see our breath," Osment told Variety. "There was a limited time that we could be in there because it was so cold and most of the scenes I'm in my underwear or something." 

 Shyamalan explained, "CGI at that time was not perfected to the place where I felt comfortable that it could do breaths. [Osment] wasn't acting, it was cold, and you could see the physicality on his skin and the way he's shivering. And even now, with CGI, I might do it the same way because of what it makes the actors do."

15. The production used the old convention center in Shyamalan's hometown of Philadelphia for many of the film's interior scenes. 

"Big, empty marble hallways, kind of a [The] Shining feel around the set itself. I believe JFK did a speech there during a campaign in 1960," Osment recalled to Variety. "It was very old and ornate and had these cavernous, marble stairways that went really deep down."

And not everyone was convinced they were there alone. "I don't know if it's just kids who make up that everything's haunted, but I'm pretty sure that place was haunted. Like, actually haunted," Barton remembered. "I don't really want to speak for Night, but I really think he kind of enjoyed it because it had this creepy air to it that made it even more fun."

16. When Toni Collette came in to read for the role of Cole's mom Lynn, she'd altered her appearance in such a way that Shyamalan was worried he'd never be able to convince Disney to cast her.

"I had seen Muriel's Wedding and Toni came in and her head was shaved, and I forget if it was for fun or if it was for a movie. She did such a beautiful job," the director recalled to Variety. "I didn't want to show the video to the studio for fear that they would be concerned with her appearance, and I said 'I want to cast the woman from Muriel's Wedding' and then Bruce backed me and said 'Oh, I love Muriel's Wedding,' so we kind of got it without the studio seeing the audition, and I was so lucky."

As for the hairdo she has in the film?

"Toni is actually wearing a wig throughout all of The Sixth Sense, and I think it's a wig from Velvet Goldmine," Shyamalan added. "We didn't even have the wig!"

17. During filming, Collette felt some spooky occurrences of her own. 

"When we were making The Sixth Sense, I had a couple of weird things happening," she told Slant Magazine in 2012. "In the hotel room I was staying at in Philadelphia, I started meditating a lot, and then I would wake up at night, roll over, and look at the clock, and it was always a repeated number—1:11, 3:33, 4:44. That started to really spook me."

18. To achieve the horrific moment when Barton's Kyra is vomiting in front of poor Cole, she was not only kept in the freezing cold—the better to see everyone's breath with, naturally—but given a very specific mixture to hold in her mouth until the time was right.

"We would make a mixture to put in my mouth. They gave me options between cereals and bananas," Barton told Variety, noting that the experience didn't really fazed her. "Everybody just asks, 'Was it traumatizing?' It really wasn't. I was already 13 and I could handle it."

19. While Collette earned herself a Best Supporting Actress nomination at the 72nd Academy Awards for her work as Collette—she lost to Angelina Jolie in Girl, Interrupted—the role was almost played by someone else altogether.

Marisa Tomei was one of the other actresses in the running, as well as some other nameless actresses with "higher profiles," according to an Urban Cinefile interview with Collette. 

20. The film proved so popular that it became the top-selling DVD of 2000. Not only that, but its worldwide gross of $672.8 million made it the highest-grossing horror film (in unadjusted dollars) until 2017's It.

Not bad for a film Disney had no faith in whatsoever.