'Miserable.' 'Dark.' 'Intense.' The Harrowing Inside Story of 'Mockingjay – Part 2's' Scariest Scene

Warning: Minor ‘Mockingjay – Part 2’ spoilers ahead

Despite shifting from the districts to the death-match arenas to the Capitol’s doorsteps and back, the tone throughout the four Hunger Games movies generally remains consistent. They’re gloomy, emotionally weighty, epic, and occasionally romantic. There’s a moment, however, in the series finale, Mockingjay – Part 2, in which the characters detour from their path, and the film’s tone takes a detour of its own.

Katniss Everdeen (Jennifer Lawrence) and her fellow Squad 451 combatants are making their way through the dark subterranean sewers of the Capitol. They hear some menacing sounds approaching. They shine what little light they have into the blackness — as viewers slide to the edges of their seats knowing good and well that the squad is about to be attacked by the unholiest of creatures. For a few minutes it feels as if we’ve been transported into a horror movie, like we’re back in the terrifying caverns of The Descent.

Related: The 'Hunger Games’ Trio Spends Some 'Buddy Time’ Looking Back at Their Globe-Spanning Life Adventure

The scene moves from tense, quiet horror to fiery, explosive action once the team is attacked by the fast, ghostly white and slimy “lizard mutts,” creatures dispatched by the Capitol’s gamesmakers to counter Katniss and her fellow rebels, including Gale (Liam Hemsworth) and Peeta (Josh Hutcherson), who are intent on capping off the revolution by dethroning the tyrannical President Snow (Donald Sutherland). More than a couple primary characters meet their demise during the ensuing battle.

All told, it may just be the best sequence in the whole series.

It was also the most miserable and most difficult sequence for director Francis Lawrence and his cast and crew to shoot. “That was really the dark period on set,” the filmmaker told Yahoo Movies. “It was rough,” echoed his lead, Jennifer Lawrence, of the three wet, uncomfortable, and injury-filled weeks spent capturing it. “It was a downer.”

The tunnels were built on a soundstage in Atlanta, but comfort was not a factor in their construction. “It’s all filled with water, and it’s all really dark,” Francis Lawrence says. “And they’re all really short, because they’re built to be claustrophobic… So everyone, crew, actors, anyone over 5-6 or 5-7 had to be ducking the whole time.”

That included the 6-foot-3 Aussie Hemsworth, who Jennifer Lawrence says didn’t stand up straight for three weeks. That was only part of Hemsworth’s aches: His fight sequences with the mutts required him to repeatedly roll over steel grates. “My hips were bruised for weeks,” he says. At another point he hurt his back after getting thrown up against the wall. Hutcherson says he cracked his knee on the grates. “Look, it’s not real,” he adds, “but you’re doing 20 different takes of these.”

But wait, there’s more! “Everybody’s wading in water,” Francis Lawrence says. “The actors are all wet. And you’re in this environment for a really long time… The water’s heated, so it created this humidity. And then you’ve got these fire bars, because we’re shooting arrows with fire, so you’ve got diesel fumes and smoke. We’re wet 12 hours a day, doing this fight choreography. It was just miserable.”

Three weeks of soaking-wet misery leads to some grumpy actors. Jennifer Lawrence remembers Hemsworth being in such a foul mood while they were drying up under the heat tent that he snapped at her after she pulled a book out of her bag. “Why do you read so much?” he asked her.

If the first part of the Mockingjay sequence feels familiar, you may have seen Francis Lawrence’s earlier work. He tapped into one of his favorite scenes from his own I Am Legend (2007), where Will Smith’s apocalypse survivor Robert Neville tracks his wandering dog into a dark space and encounters “the infected.”

“I just thought that really worked in terms of suspense,” the director says. “I really liked that I could play around with some of those ideas in the tunnels before the creatures come out. Once the creatures come out, it was a completely different ballgame and it was different story beats that needed to happen, how the crowd gets separated. It was more about the chaos and the loss. And so it all really changes gears and it goes from something scary to something intense and emotional.”

Stuntmen in green suits played the lizard mutts on set, while go-to New Zealand special effects house WETA added the actual animated creatures. The re-creation of the mutts’ action movements, with actual splashing and grabbing, added authenticity to the scene, the director says, even if the stuntmen didn’t exactly scare his actors. “In real life they looked goofy,” Jennifer Lawrence says. “They’re laughable.”

At least the actress had something to laugh about over those three weeks.

The Hunger Games – Mockingjay Part 2 is now in theaters.

Watch Jennifer Lawrence talk about some of the series’ best stunts: