TL;DR: Beware Boiúna has a great mythological monster, likeable leads and a few nasty highlights, but its slow start, cluttered side plot and severe lack of snake time leave it only just serviceable.

Giant animal movies make a simple promise: take something that already makes your skin crawl, scale it up to kaiju proportions, and let chaos follow. Beware Boiúna takes that promise into the Amazon. Three doctors arrive on a humanitarian mission to provide medical care, travelling by boat with a small crew, and end up in the territory of Boiúna, a colossal serpent from Brazilian mythology. She isn’t written as a hungry predator so much as a force of nature that removes anyone who disturbs the balance of her home. That’s a strong hook, and it gives the film a mythic flavour that most “big thing eats people” movies never try for.

Director Mike P. Nelson, recently tapped to helm the eleventh Saw film, works from a script by genre veteran Alan B. McElroy, with Jessica Rothe, Kiana Madeira, Logan Marshall-Green and Will Close leading the cast. The film opens in theatres on October 2 through Constantin Film. On paper, it has everything a Friday-night creature feature needs. In practice, the movie keeps its biggest asset hidden for far too long, and that one decision ends up shaping almost everything I think about it.

The slow boat ride drags down this monster movie

Pacing is the main problem. At 104 minutes, Beware Boiúna feels like it could lose a quarter of an hour without anyone noticing, and most of the excess sits in the first act. There are a couple of early kills to signal that something big lives in the water, but then the film spends a long stretch on character dynamics and a deliberately grounded, serious tone. I respect the ambition. Themes about the exploitation of the Amazon and its Indigenous people fit a story about a guardian spirit punishing intruders, and the idea has real potential. The trouble is that the film delivers these themes in long, separate blocks instead of building them into the action, so the message and the mayhem take turns instead of strengthening each other.

A side plot makes the drag worse. Med student Alli (Rothe) and ship mechanic Lena (Madeira) go through a dark experience that sends Brennan (Marshall-Green), a “colonizer” figure, and his men chasing them in a second boat. It adds tension and, yes, more snake food, but it feels imported from a grittier survival thriller. Like playing a side quest before the boss fight is even unlocked, it isn’t bad on its own terms. It just stands between you and the thing you came for.

Boiúna is impressive, when the camera lets you see her

Once Boiúna arrives, she looks great. The film understands that her sheer size is a weapon, and a moment where she smashes into a construction vehicle has the right Shadow of the Colossus sense of scale, where the creature is less an animal than a piece of moving landscape. Cinematographer Nick Junkersfeld gives the river and jungle a handsome, atmospheric look, and the effects hold up well in the shots where the serpent is clearly visible. That’s the frustrating part. Every good glimpse makes you want more, and the film rarely delivers.

The limited budget shows. Boiúna stays offscreen or half-seen for long stretches, and in places shaky-cam is used to hide what the effects can’t afford to show. Withholding the monster can work beautifully when the tension carries the scene, as Godzilla 2014 and Cloverfield showed by turning absence into dread. Here, the absence feels like a budget limit rather than a creative choice, and the suspense doesn’t build enough to cover the gap.

Alan B. McElroy plays games with the body count

McElroy’s script is the film’s most interesting element. It deliberately disrupts the familiar creature-feature rhythm, muddying who dies next, whose point of view you’re following, and which character you’re supposed to root for at any given moment. For anyone who has seen enough of these films to predict the death order from the opening boat scene, that unpredictability is refreshing. Unfortunately, many of the kills themselves fade from memory quickly. Too many characters die fast and without a distinctive detail, so they feel like Tremors-style bystanders who never got a proper scene.

When the film commits, though, it lands some properly nasty moments. A scene involving mosquito eggs left inside a person’s back is pure body horror, and the best sequence has a character improvising a survival plan using a dead friend’s corpse. That scene is clever, grim and tense, and then the film immediately follows it with flashbacks reminding us of a relationship we already understood. It’s a perfect example of the movie’s constant tug-of-war between smart instincts and unnecessary hand-holding.

Jessica Rothe, Kiana Madeira and Will Close keep the cast afloat

The leads are a big reason the film stays watchable during its slow first half. Rothe and Madeira make Alli and Lena believable survivors, people who think quickly and act sensibly rather than wandering into the water for no reason. Their resourcefulness gives the audience someone to trust, which matters in a genre full of characters who seem to want to die. Will Close is the scene-stealer as Callum, a comic-relief character who is out of his depth long before a serpent shows up. He makes every funny line count, and the film badly needs his energy whenever the tone becomes too heavy.

Nelson’s direction has some real flair, too. One jump scare uses blurriness as a setup in a way that genuinely surprised me, and several scenes have the kind of “okay, that was cool” craft that suggests he can handle Saw’s demands. The trouble is that these highlights never connect into sustained momentum, so the film feels like a strong highlight reel rather than a ride that pulls you along.

Verdict

Beware Boiúna has more ideas than the average giant-snake movie, from its mythological creature and environmental themes to a script that enjoys toying with genre expectations. Rothe, Madeira and Close are good company, the visuals are attractive, and a handful of set pieces deliver memorable creature-feature thrills. However, the bloated setup, distracting side plot, forgettable deaths and, above all, the stingy screen time for its title monster keep it from being more than passable. Hardcore creature-feature fans and anyone curious about Brazilian folklore on the big screen may find enough to enjoy. Everyone else should probably wait for streaming.