Two men wake up in an abandoned industrial bathroom, each chained to a pipe. When they find a hacksaw in the toilet tank, they try to escape from the thick chains but fail.

That’s when the doctor, played by Cary Elwes, comes to a realization about his kidnapper, bringing this impossible “Saw” choice into visceral focus: “He doesn’t want us to cut off our chains. He wants us to cut off our feet.”

“Saw,” released 20 years ago this week, was never expected to be a success. It was a low-budget calling card for two Australian film students who wanted to start their careers with a small jump and a good idea: a serial killer who forces his victims to prove they want to survive through bloody sacrifices.

Instead, it grossed more than 80 times its budget at the box office, creating a horror villain for the new millennium and inspiring the “torture porn” label, with each subsequent installment in the series further increasing revulsion.

Two decades later, it can be hard to remember that the original “Saw” was more concerned with morality than gore.

“What would you do to save your life or the life of someone else?” said actor Shawnee Smith, summarizing the central tension behind the series’ elaborate trappings. In “Saw,” Smith’s character has to find a key into another person’s stomach to quickly escape the “reverse bear trap” surrounding his head. Sleepy but still alive.

Elwes, known for his role as Westley in “The Princess Bride,” said he was drawn to “Saw” because it was a horror story filled with ethical and moral questions.

“This is a thinking man’s thriller,” he said.

The seed of the idea that became “Saw” was simple: two men locked in a room and a body lying between them. Classmates James Wan and Leigh Whannell from the Royal Melbourne Institute of Technology’s film school were considering developing their first feature film and bounced ideas around until one stuck. They wrote the script together and Wan directed it.

Wan, who has made mind-blowing horror films such as “Insidious” and “Malignant” as well as big-budget Hollywood films, said “Saw” turns classic tropes on their head.

“Oh, did you see that? Oh, you think you know what’s going to happen?” Wan said he made a fitting tribute to “Saw” from a dingy basement bathroom in London, the only place he could get cellphone service while filming the next installment of “The Conjuring” franchise. “I’m going to try something else you haven’t seen before.”

Classic tropes from “Saw” (serial killers, haunted detectives, creepy puppets) are brought together and inverted around the undeniable duo of its central predilection.

Unlike the dazzlingly meta horror films that came before it, including the horror-buff teenagers of “Scream” and the Rube Goldberg machinations of “Final Destination,” no amount of genre savvy can save “Saw”’s characters from having to make a final decision.

Film critic David Edelstein described “Saw” and some of its ilk (most notably Eli Roth’s “Hostel” (2005)) as “torture porn.” 2006 New York magazine article. But the first “Saw” isn’t all that gruesome compared to this year’s deaths. “Scary 3” And “In the Nature of Violence.”

“Saw” is more of a crime thriller with a scary twist. While the aforementioned device acts as a rusty Chekhov gun, the desperation of the characters creates horror.

The series’ traps were designed by the character John Kramer (Tobin Bell), a terminally ill cancer patient who is angry at people for wasting their lives. Kramer, who would eventually be known as Jigsaw, is not technically a serial killer. Each victim is given the choice to live.

“Deep down, John is in the business of saving souls, although he can be a little ruthless in his approach,” Bell said.

This framework emerged from Whannell’s personal experience with recurring migraine headaches in her early twenties. As he sat in the waiting room before his CT scan, he wondered how a diagnosis of an aggressive brain tumor could change someone.

Whannell, who plays the second man trapped in the bathroom, said of the killer’s motive: “It looked like it was game time. “He gives them this time and says, ‘How badly do you want to live?’ “It makes them do extreme things like that.”

“Saw” had no simple path to creation. When it came time to make the film, Australian financing fell through.

Wan and Whannell were willing to save money to film on the cheap, but Whannell’s manager, Stacey Testro, thought it might work in Hollywood, where she also has an office. Instead of sending it to court producers in the United States with just a script, the writers 10 minute short film The reverse bear trap sequence with Whannell on the rig.

Testro remembers watching the short film in his living room, with his luggage by the door and a car waiting to take him to the airport. “It was very exciting,” he said.

Producers Gregg Hoffman, Oren Koules, and Mark Burg of Evolution Entertainment were impressed enough to give Wan and Whannell a $700,000 shooting budget for the chaotic 18-day shoot; this kept costs down by shooting mostly on the bathroom set. Wan, who previously focused on stop-motion animation, also handcrafted Billy the Puppet, a disturbing ventriloquist dummy with red spiral cheeks, a tricycle, and the series’ most famous line, “I want to play a game.”

Wan used papier-mâché for Billy’s eyes, ping-pong balls, and cardboard boxes to fill a child-sized tuxedo for the body. (Wan said at first that he also had a bowler hat, but it looked a little too silly.)

The limited budget did not prevent the film’s ideas from resonating with audiences.

“The first movie was all about ethics and how far you can go and what’s right and wrong in humanity,” Burg said, recalling that Evolution thought “Saw” would be a version of David Fincher’s “Se7en” (1995).

Whannell described his goal for “Saw” as a mix of “Se7en” and “Cube.” In Fincher’s film, Brad Pitt and Morgan Freeman are detectives pursuing a serial killer who models his murders after the seven deadly sins and punishes his victims with complex fictions that symbolize their moral failings. In Cube (1997), an offbeat Canadian science fiction horror film, inmates in a mysterious prison move through rooms rigged with traps.

The expanded “Saw” series, the 11th film scheduled for release next year, hasn’t always stuck to the ideas put forward by the first movie. Wan never directed another “Saw” movie, while Whannell contributed to “Saw II” and wrote the screenplay for “Saw III.”

In the decades since the release of “Saw,” Wan has directed major franchises such as “Aquaman” (2018) and “Furious 7” (2015). Whannell has also directed films including “The Invisible Man” (2020), starring Elisabeth Moss, and the upcoming “Wolf Man,” both modern incarnations of classic horror stories.

This success goes back to two friends, novice filmmakers who tried to come up with a compelling story and then made ethical choices that had bloody consequences.

Whannell is most proud of the “Saw” franchise’s enormous impact on popular culture. Favorite thing: In “The Sopranos,” a character focuses on promoting a movie that combines “Saw” with “The Godfather Part II.” Billy the Puppet was recently added to the popular battle royale video game Fortnite.

“Whether we wanted to or not, we’ve basically created the Freddy Krueger of millennials,” Whannell said.