- The opening credits
, set to a cut from Thomas Bangalter's soundtrack for the film titled "Tempus Edax Rerum". The film's strobing text combines with the track's drum beat and industrial noise to generate suspense for the film before it even begins. - Alex's assault at the hands of Le Ténia. That's nine minutes of uncut, graphic rape, and then the brutal beating afterwards that disfigures Alex's face. To this day, it is still considered one of the most disturbing sequences in film history.
- As Alex is being raped, someone wanders into the underpass in the background. They stand there, watching what is happening, and you hope they'll offer help. And then they turn around and walk away.
- The entirety of the Rectum scene.
- The chaotic atmosphere the club creates is nauseating enough, with the dense population of men and overbearing wash of red lights.
- When Marcus and Pierre try to find Le Tenia, Marcus attacks the man they mistake for the rapist (standing right next to him), but the man ends up wrestling him to the ground and graphically breaking his arm (all of which is shown on camera).
- When the man then attempts to rape Marcus, he gets a fire extinguisher directly to the face from Pierre. He then proceeds to bludgeon the man's face with it over, and over, and over, and over, all while he screams at him to stop, the man continuously moans, twitches and gurgles for air, and some of the club attendees cheer Pierre on in the background. By the end, while we see the man's face is horrifically caved in, we can hear him weakly gurgling — he's still alive. Though he presumably didn't live for much longer after that, the fact that anyone could live through a beating like that for any amount of time is deeply disturbing.
- The specific way Noé chooses to depict the beating — the camera follows the extinguisher's exact motions, intensifying the effect of each impact, and even flips upside down several times to make for as disorienting a watch as possible.
- All of this is scored by Bangalter's nightmarish track "Rectum", which consists of an oppressive, cyclical Drone of Dread, which is later coupled with frenetic drum-and-bass, and has been described as "if a panic attack was converted into music".
- The film's closing (or chronologically opening) moments — an eye-searing sequence flashing frantically between white, open sky and a tumbling shot of black space as the industrial roar of "The End" plays, slowly mounting in volume until, at its ear-splitting climax, it just snaps to pure, void silence as the film's core message flickers on screen:"LE TEMPS DETRUIT TOUT" ("TIME DESTROYS EVERYTHING")
- Other tracks from Bangalter's soundtrack noteworthy for their NF factor:
- "Irreversible", a foreboding piece with swirling horror synths that sound like you're being welcomed into a vampire's lair.
- The aptly-named "Stress" and "Outrage".
- "Irreversible"
- The "new trailer" for the chronological "straight cut" of the film does a pretty good job at capturing the film's dread in only 96 seconds.
- The chilling mashup of "Tempus Edax Rerum" with Beethoven's 7th (which plays over the finale) that soundtracks the opening.
- The trailer's ending. The image of Alex about to enter the fateful underpass is displayed with an artificial strobe effect that slowly goes away. As she walks through, the strobe returns moments before we see a figure just rounding the corner, and the trailer cuts away. For those who already know what happens next, the sheer implication of it is haunting.
