The actors were given no more than a 35-page outline of the mythology behind the plot before shooting began. All lines were improvised and nearly all the events in the film were unknown to the three actors beforehand, and were often on-camera surprises to them all.
Some theatergoers experienced nausea from the handheld camera movements and actually had to leave to vomit. In some Toronto theatres, ushers asked patrons who where prone to motion sickness to sit in the aisle seat and to try not to "throw up on other people."
This film was in the Guinness Book Of World Records for "Top Budget:Box Office Ratio" (for a mainstream feature film). The film cost $22,000 to make and made back $240.5 million, a ratio of $1 spent for every $10,931 made.
The three leads believed the Blair Witch was a real legend during filming, though of course they knew the film was going to be fake. Only after the film's release did they discover that the entire mythology was made up by the film's creators.
The filmmakers placed flyers around Cannes for the film festival that were "Missing" posters, stating that the cast was missing. All the flyers were taken down by the next day. It turns out that a television executive had been kidnapped just prior, and they were taken down out of respect. The executive was since recovered safely.
In a scene where the main actors are sleeping in a tent at night, the tent suddenly shakes violently and they all get scared. This was unscripted and the director shook the tent; they were really scared.
When the movie was released the town of Burkittsville, in the hopes of making at least some profit from the film, did its own marketing. During the annual summer carnival the local Ruritan Club featured the "Bur-Witch" sandwich - country fried ham and a fried egg on top of a cheeseburger, nestled in a sesame seed bun, and doused with horseradish. The sandwich was the most popular selling item on the menu two years in a row.
In the movie, Heather and Mike share a somewhat antagonistic attitude towards each other. In the commentary, the directors revealed it was Heather and Joshua who were arguing most of the time (and more heatedly). Almost all of the footage of their arguments was taken from the final cut after the filmmakers decided it seemed like both men were "ganging up" on Heather.
The 1999-2000 hunting season suffered badly due to this film. The movie was so popular that fans all over the country were hiking into the wilderness to shoot their own Blair Witch-style documentaries. As a result they kept most of the wildlife scared away from hunting areas.
The runic lettering in the old house are a mixture of two different alphabets, Hebraic and Futhark. Hebraic runes went on to become Ancient Hebrew. Futhark runes are proto-European, dating from the first millennium B.C.
The directors put up posters at a local college in an attempt to recruit students to help work on this low budget production. Only one person responded to the recruitment ad, and this was Patricia DeCou, who not only portrayed Mary Brown, but also helped with the art department.
Although having been given a brief crash course on using the 16mm camera, Joshua Leonard struggled to focus using it for the first few days of filming. This is why the interview with Mary Brown is of such poor focus and incredibly grainy.
Although Heather, Mike and Josh had to pitch and take down the tent they slept in, they did not have to carry it from location to location for them as this was done for them by the movie crew who would do so out of sight.
Heather Donahue admitted there was a considerable backlash against her because of her association with The Blair Witch Project. It led to her having threatening encounters and difficulty finding other employment.
The two fishermen were father and son in law. Sanchez and Myrick toyed with the idea that one of them was playing a prank on the kids, like something out of Scooby Doo, Where Are You!. They didn't follow through with it because it seemed a cheesy reason for all the spooky goings on.
Sanchez and Myrick wanted Heather to have a sort of Captain Ahab quality (obsessively documenting everything). Heather Donahue had that. Mike's function in the film is to say the things the audience is probably thinking. And Josh (for a time) is the team peacemaker.
According to the directors, the scene where Heather, Josh and Mike were in the motel room was the longest piece of film that the three had shot. The scene reportedly went on for at least ninety minutes and involved Josh and Mike reading poetry followed by some drunken arguing between Josh and Heather.
In the initial draft, Josh was intended to have a strong romantic interest in Heather. In several of the scene instructions given to the actors on the callback auditions, it was instructed that Josh take note of how attractive Heather was, and how dejected he should be that she seemed oblivious to this. Eventually the idea was scrapped as fear the movie would become too cliché.
Heather Donahue's discovery of Joshua Leonard's teeth, blood and hair wrapped in a bundle of twigs bears a striking similarity to Washington Irving's story "The Devil and Tom Walker". Tom's wife goes to find the devil in the swamp, and never returns home. When Tom goes to find her, he discovers her apron with her heart and liver inside. However, it also reflects a scene in the silent documentary "Haxan" where a severed hand is carried by a witch hidden in a bundle of twigs.
Other endings shot in post-production that were scrapped included Mike being hanged, another had him bound to the wall with twigs in the manner of a stick figure. Stick figures themselves were experimented with as decorations in the final scene.
This film was one of the most pirated films of 1999 because of limited release due to its independent status. The pirated version was an unfinished leaked work-print with several plot holes and most of the initial interviews missing leading to audience confusion at final scene of the film.
When Heather screams "What the **** is that?!" she is seeing one of the movie crew standing on a hill dressed in white with a ski-mask on. Mike was holding the camera as ran behind her and didn't manage to catch the image on film.