In one of Evan's flashback scenes he is heard reading an excerpt from Ray Bradbury's short story "A Sound of Thunder". In that tale a group of people travel millions of years back to hunt dinosaurs; one of them accidentally treads on and kills a butterfly, which dramatically alters the future.
All the prison scenes were filmed in an actual prison in the state of Washington with real inmates.
Evan's mother mentions that she suffered late-term miscarriages before Evan was eventually born. That detail does more than set up the alternative ending — where Evan watches footage of his birth and strangles himself whilst still in the womb — it also invites speculation about whether those losses were natural or whether Evan might have had siblings who experienced the same fate and chose to take their own lives shortly before being born.
In early drafts of the screenplay, the character who became Evan was originally called Chris Treborn. When the letter "T" is moved, it forms "Christ Reborn". The name was later altered to Evan Treborn, intended as a pun on "Event Reborn".
There are four alternate endings. Most of them involve Evan and Kayleigh having a chance encounter as adults in a timeline where they never knew each other as children. In the first, Evan turns and speaks to Kayleigh at the same moment. In the second, Evan turns only after Kayleigh has already turned and then follows her. The directors referred to this as the "happy sappy stalker ending" and said that if the studio had insisted on including it in the cinema release, they would have publicly distanced themselves from the film. In the third ending, Kayleigh turns first, then Evan turns, and Kayleigh walks away; Evan stands for a minute, then walks off and does not follow her. The directors called this the "happy sappy ending" and described it as the minimum ending they would accept for the cinema release if the studio insisted, since at least Evan learns *some* lesson about self-sacrifice. In the fourth, Evan watches a home movie of his birth instead of meeting Kayleigh; he travels into the footage and strangles himself in the womb. (This can be seen at the end of the Director's Cut.) This was always the directors' preferred ending, but the studio deemed it too grim for the cinema release, which instead features the ending where Evan tells Kayleigh off at a childhood party, preventing any relationship from developing.
Ashton Kutcher undertook extensive research into psychology, mental disorders and chaos theory whilst preparing for his role in this film.
It was one of the most widely read unproduced scripts in the industry. The project did not receive the go-ahead until writers/directors Eric Bress and J. Mackye Gruber agreed to write Final Destination 2 (2003), and Ashton Kutcher came on board as an executive producer of The Butterfly Effect.
Elden Henson filmed all of the later 'normal' scenes with his character first because he had to gain around 20 pounds in a month for the subsequent timelines in which his character is unhinged. He was intended to look bigger as the unhinged Lenny and thinner as the 'normal' Lenny. To the filmmaker's astonishment, he achieved it.
The lights in the background of the psychiatrist's office flicker while Evan is being hypnotised, after they blew up the mailbox. This wasn’t a planned special effect — it was caused by an actual short in the on‑set wiring. The directors thought it suited the scene and kept that take in the film’s final edit.
They only had three post boxes to blow up, and they only succeeded on the third attempt.
The sequence in which Evan has no arms was produced using two separate shots: one showing an empty bed and another featuring Ashton Kutcher lying in the bed wearing green gloves (which were erased afterwards). Both takes used identical camera movement. On most films this would be achieved with machine- or computer-controlled camera rigs that can replicate the exact same motion across multiple takes. However, as the film was relatively low-budget, the production couldn't afford such kit, so the two matching shots were obtained by moving the camera manually while timing the moves with a stopwatch. Any minor discrepancies between the two shots were fixed digitally in post-production.
Logan Lerman (playing Evan at age seven) wore dark contact lenses to match Ashton Kutcher's eye colour.
In the original ending, Evan travels back in time and takes his own life as an unborn foetus in his mother's womb. That ending was used on the Director's Cut DVD. For the cinema release the film was given a different ending: the conclusion was altered so that Evan goes back to the day he first met Kayleigh as a child and upsets her by telling her he hates her and her family and threatening to kill them all if she comes near him again. Evan does this because he believes the only way for himself, his family and close friends to be happy is to avoid any contact with Kayleigh or her troubled, overprotective brother Tommy. By doing so Kayleigh and Tommy are able to live with their mother rather than remain with their father and suffer abuse, which had set off the original chain of events. As Kayleigh explains earlier in the film, her desire to be near Evan is the reason she did not go to live with her mother.
There is a scene in which an alternate reality is created where Evan finds himself at university as a member of a fraternity. While his memory is being 'rebuilt', Kayleigh gets a lift to visit Evan at age 13 after he had moved away. People don't realise (and it isn't even mentioned in the DVD commentary) that the driver is Karl, the bald inmate who would exist in that timeline before being sent to the same prison as Evan.
The title alludes to a notion in chaos theory that small events can, unpredictably, lead to much larger outcomes. The opening quotation makes this point by suggesting that a butterfly's wingbeat might culminate in a typhoon. In a secondary sense, it can also be read as an allusion to the short story "A Sound of Thunder" by Ray Bradbury.
The film's title screen shows a frontal scan of the brain. In that image the left and right lateral ventricles around the corpus callosum (the central part of the brain) appear displaced. This is something seen in many patients with schizophrenia. The displaced central ventricles are sometimes said to resemble a butterfly. In the film Evan is not schizophrenic, but in the penultimate universe he "jumps" to (after he accidentally causes Kayleigh's death as a child) he is treated as if he were; the doctors tell him that everything that occurred over the course of the film was fabricated.
Evan's diaries share the same cover design as John Doe's notebooks in Se7en (1995), a film that was also released by New Line Cinema. They are ordinary composition notebooks used by schoolchildren across the country every day.
When Evan regains consciousness in the sorority house, a 'Bradbury University' pennant hangs on the wall — a nod to Ray Bradbury.
The wig donned by Eric Stoltz for the film was fashioned from his own real hair.
The film is set in 1989, 1995, 2002 and 2010.
The teenage incarnations of Evan, Kayleigh and Tommy go to see Se7en (1995) at a cinema that is also screening Dumb and Dumber (1994). Both of those films, as well as this one, were released by New Line Cinema. Elden Henson (Lenny) and William Lee Scott (Tommy) both appeared in Dumb and Dumberer: When Harry Met Lloyd (2003).
Hanging above Evan's bed in his room at the hall of residence is the painting 'Sleep' by Salvador Dalí.
In the sequence where Evan and his mum are standing at Jason's graveside, Kayleigh approaches and takes Evan's hand. Because the shot is framed from a distance and the soundtrack is playing over the moment, her words are indistinct. In fact, she says: "You're probably better off now."
Josh Hartnett, Seann William Scott and Joshua Jackson were each offered the part of Evan.
Evan's cigarette-burn scar closely resembles the outline of the Mandelbrot set — a motif often used to represent chaos theory that underpins the butterfly effect.
Aside from a fleeting, split-second appearance in a photograph during the penultimate 'jump-back', co-director Eric Bress can also be seen at the start of the film as a patient in a psychiatric hospital. In the director's-cut alternate ending he also makes a cameo as Andrea's new husband in the alternate time line created by Evan.
The film's protagonist, Evan, recorded roughly ~4,745 entries from age six through 19 (essentially 365 days x 13 years). Allocating those 4,745 entries across 192 pages (both sides) of a standard notebook works out to about 24 notebooks in the film.
During Evan's penultimate flashback (the one after which he awakens in the psychiatric hospital), a rapid succession of shots shows people pulling funny faces. One person who appears in several of the pictures is co-director Eric Bress.
Ali Larter was offered the part of Kayleigh, but later pulled out.
Tommy could be living with antisocial personality disorder.
The fraternity-pledge sequence was shot on the lawns of the historic Ceperley House on the shores of Deer Lake in Burnaby, BC, Canada. Evan's proposal was filmed in front of the property's gardener's cottage, situated behind the main house. Coincidentally, the mansion actually served as a fraternity house for SFU for a short spell in the 1960s, until the city of Burnaby evicted the students to convert the residence into an art gallery. Defiant students barricaded themselves inside and set the living room alight.
"butterfly effect" denotes the idea that major future events can be altered by something seemingly trivial, such as stepping on a butterfly or — in the introduction to this film — a butterfly beating its wings. The concept comes from Ray Bradbury's 1952 story 'The Sound of Thunder'. In that tale a time traveller joins a safari to hunt dinosaurs. The particular creature they target is known to be destined to die within minutes when a tree falls, so its death is deemed inconsequential; the hunters are suspended above the ground on a projected path and wear hazmat suits, but one man panics, slips off the path and the hunt is ruined. On returning to the present he finds history has taken a disastrous turn. As he removes his hazmat suit he notices, embedded in the mud on his boots, a crushed prehistoric butterfly. The 'sound of thunder' is the gunshot he fires himself.
Ethan Suplee (Thumper) was genuinely as overweight as portrayed. He subsequently underwent an intense, prolonged fitness and dietary programme that completely transformed his physique.
While Evan is making a call at "State", he dialled 555-5785 — a number that Frank Rizzo of The Jerky Boys frequently repeats.
The Hilltop Café, where Kayleigh (Amy Smart) works, was also used as a location in Bates Motel (2013). In Episode 2.2, Shadow of a Doubt (2014), Dylan (Max Thieriot) and Bradley (Nicola Peltz Beckham) are shown waiting there for the bus.
Kevin G. Schmidt (the 13-year-old Lenny) and Ashton Kutcher (the adult Evan) had both previously appeared in Cheaper by the Dozen (2003).
Evan's final note would be irrelevant if he were to asphyxiate himself in utero (which would be impossible for a foetus), because by erasing his existence before birth he would be unable to write the note.
Elden Henson (Lenny) goes along with his mates expecting to see the comedy Dumb and Dumber (1994), but ends up watching a different film. Henson later turns up in the follow-up to that picture, Dumb and Dumberer: When Harry Met Lloyd (2003).
Evan is a member of the fraternity house called Chi-Phi-Beta, a subtle nod to the film's science-fiction themes.
The final ending chosen by Eric Bress and J. Mackye Gruber was an homage to the 1980s Japanese classic The Girl Who Leapt Through Time (1983), the adaptation of Yasutaka Tsutsui's novel of the same name. The final sequence in which the characters meet but do not immediately recognise one another is essentially identical in both films.
It remains the only film in the Butterfly Effect series to receive a cinema release. Its sequels, The Butterfly Effect 2 (2006) and The Butterfly Effect 3: Revelations (2009), were issued straight to DVD with new casts.
