When Ashley has the Bughuul's super-8 camera in her hands, it is a Pro8mm camera. Pro8mm's cameras are hybrid cameras, usually Bealeau versions, from the 1990's onward. It is stated that the Bughuul has been using the same camera since 1966, but the kind of camera Ashley is holding was designed in the 21st century so this wouldn't be possible.
Items, products and family belongings seen in the super 8 home movies often weren't available in the decades that the home movies are set in. Most notably is the kitchen refrigerator seen in the 1998 'Sleepytime' home movie reel - the model of fridge shown in the home movie wasn't available commercially until 2009-2010.
At the end of the film, just after Ellison has been knocked out when finding the substance in his drink, he collapses to the floor, then Ashley appears. She says "I like how you made the movies longer, they're better this way" but her mouth doesn't move.
Ellison states in the movie that 8mm film was invented in 1966 by Kodak Inc. but this is incorrect. 8mm film was invented in 1932 for home movies. Super-8 film (the film type actually used to film the murders in the movie, not 8mm contrary to Ellison's statements), was invented and sold for home use in 1965, a year before 1966. There was no type of film invented in 1966.
Near the beginning of the film, we see Ashley painting a girl in red on the wall. We see that Ashley has painted the girl fully in red, however, in the next shot we see that the girl has a white space where the red paint was before.
When Ellison watches the BBQ '79 film on his computer, after filming it with a digital camera, the clip of Bughuul seen in the window is longer than what it was when Ellison first watched the original film.
Throughout the movie it is mentioned that the snuff movies were filmed on 8mm film reels. However, according to director/writer C. Robert Cargill, Super-8 film was used. There isn't a whole lot of difference between film types but Super-8 is slightly different and considered better for filming home movies. 8mm film is harder to obtain than Super-8 film.
Pennsylvania's county sheriffs departments do not conduct routine patrols. Their main focus are courts and prisons. The Pennsylvania State Police conducts patrols in municipalities that do not own their own departments.
When Ellison finds the undead children in the attic watching their super 8 movie, they all appear to be in various states of decay. Stephanie, who was killed in 2011, has decayed more than the other children, who died decades before she did. The boy who was killed in 1968 looks nearly the same as he did before, yet the boy who was killed in 1979 has a face blue-green with mold and rot. Bodies that have been dead longer decay more than recent bodies.
As Ellison views all the super 8 home movies, they all have excellent lighting, everything is visible. It is stated that the films were made in the night when the murders took place. Super 8 cameras are unable to record at night with the camera alone, the film would only capture a black haze. For the home movies to have the lighting that they had, the murderer would have had to have the time to order and set up proper lighting equipment around the victims.
Ellison finds a scorpion in the attic of the house when he first ventures up there. We find out later that the house is in Pennsylvania. Scorpions, mostly found in subtropical climates, are not native to Pennsylvania. When Ellison mentions it to the deputy, he reacts as if it was a normal occurrence, rather than pointing out that it would have had to have been planted there.
One of the last scenes, Ellison retrieves firewood from outdoors, where it is raining. He then proceeds to make a perfect, non-smokey fire. This is impossible given the humidity that would have seeped into the wood.
When Ellison finds the children in the attic watching one of the Super 8 films, Bughuul suddenly appears on camera and jumps out at Ellison, but his reaction to the scare is delayed about one or two seconds.