When Evil Lurks

• Director Demián Rugna began developing the concept in 2018 while working on the Terrified remake — the script then won the Runner-Up Prize at the Sitges Pitchbox in 2021 before the film shot in 2022, a real but far shorter road than "over a decade."
• Rugna used no CGI on the film at all — the grotesque transformations and gore run roughly 85% practical effects and prosthetics, which he's said he prefers because he doesn't fully trust CGI on a film this size.
• The film's brutality (including violence involving children) would likely have earned an NC-17 from the MPA, but it skipped that process entirely — Shudder and IFC Films released it unrated (NR) in US theaters and streaming in October 2023.
• When Evil Lurks won Best Feature Film at the 56th Sitges Film Festival in October 2023, becoming the first Latin American film ever to take that prize in the festival's history.
• Rugna has named The Road, the Korean film The Wailing, and Evil Dead as direct touchstones for the film — not Lucio Fulci, though critics have widely compared its unrelenting gore to Fulci's Italian horror.
• Rugna confirmed in a 2024 interview that a sequel script already exists and is finished, with the project currently waiting on funding rather than being in active production.

The 'demon' is not a supernatural entity so much as a metaphysical pathogen that exploits the specific moral failings and hidden resentments of each host, suggesting the community was already rotting from within before the infection arrived.

The cyclical nature of the ending implies that the brothers' attempt to contain the evil actually accelerated its evolution, turning them into patient zeros for a wider spread rather than saviors.

The film pointedly gives its characters only folk ritual and inherited superstition to fight with, no priest or church ever shows up to help, suggesting a universe where organized religion has already lost and only scattered, half-remembered tradition is left standing against something purely entropic.

Two brothers in rural Argentina stumble onto a "Rotten" — a person housing an unborn demon waiting to be birthed — and one bad decision about what to do with him triggers an infection that spreads like wildfire through their isolated community. This isn't possession in the usual sense; violence against the infected only multiplies the corruption, jumping from person to person, animal to animal, faster the more anyone fights back. As the outbreak escalates, the brothers realize there's no priest, no exorcism, no authority coming to save them — just an old ritual, a closing window before the demon is fully born, and a choice about how far they're willing to go. The film dismantles the sanctuary of the family unit, proving that once evil breaches the doorframe, survival demands becoming just as monstrous as the threat hunting you.