Continuity mistake: When Nicholas Cage is being escorted to fetch the roll of film from his car, there are a few scenes where the accountant is holding a gun to Nicholas's head. When the camera is directed at the accountant, two hands can be seen grasping the gun, but when the camera is facing Mr Cage, initially there are two hands but after the next switchback there only appears to be the one! (01:20:50)
Continuity mistake: When Nick Cage picks his daughter up to stop her crying at the beginning of the movie, he rests her head on his right shoulder. But when he turns around to tell his wife that he loves her, her head is now resting on his left shoulder. (00:06:10)
Continuity mistake: After Machine cuts Max's throat, Welles runs toward him and is thrown down by Machine. Then the shot cuts to Poole (Gandolfini) kicking Welles with Machine running up. Then a shot or two later when Machine and Poole are beating Welles it cuts and Poole is kicking Welles and Machine is not around. (01:22:10)
Audio problem: Right after Max and Tom watch the two fake snuff films, Max mentions the record company's lack of interest. At one point his lip movements don't seem to match his words. (00:50:35)
Other mistake: After Cage calls Gandolfini and tells him he knows about the murdered girl, Gandolfini uses the telephone. There are 13 beeps, then Cage replays it and there are 12. Telephone numbers even with the "1" and area code, only have 11 numbers. (01:01:10)
Other mistake: In the scene where Max is all beaten up, Machine slashes his throat and you can clearly see that the knife's blade is dull, because there's no cut or blood. (01:21:55)
Audio problem: When Machine's mom was telling him she'd really hope he'd go to church with her tonight, her mouth was saying something completely different.
Continuity mistake: When Dino is burning the film, Welles is handcuffed to the bed. However, his handcuffs move from the outside the first T of the bed to between the first and second Ts on the bed. (01:22:35)
Revealing mistake: When Machine slits Max's throat no blood comes out of the wound. (01:21:55)
Continuity mistake: At the end, in a fight with the machine, Nick Cage sees his gun outside the fence. When he reaches for it, now it is a knife, and after he retrieves it, he now has the gun.
Continuity mistake: When Tom and Eddie get to the building where Mary Anne was killed, it's dark outside, yet when they walk through the door, it appears to be daytime.
Visible crew/equipment: When Tom goes to talk to Max the second time at the porn shop, just as he gets to the counter, you see the boom mic on the left top of the screen.
Character mistake: Throughout the whole movie, Mary Anne has an e at the end, yet in the note her mother wrote to Tom, Anne has no e at the end. It even has an e at the end in the ending credits.
Character mistake: Mary Ann's mother's name is Janet. At the end when Tom is reading the note she wrote, she misspells her own name as Janent.
Continuity mistake: After Tom has broken into Machine's house and begins to go up the stairs from the basement, we catch a quick glimpse of Tom's pistol. The pistol doesn't have a silencer, but, as he begins the climb up the stairs it suddenly appears. (01:50:20)
Answer: A snuff film is a movie where someone is actually killed on film, where the intention is to sell the movie afterwards. There are several other instanses where people are shown murdered on film (news reports, the Zapruder film, dictatorships documenting executions, etc.), but if the purpose of making the movie is not commercial, it is not a geniune "snuff" film. FBI experts and other law agencies state that they have never seen a genuine "snuff", and that it is most likely just a rumor, especially since the concept of someone willingly selling evidence of their own crimes to strangers and remaining undetected for 30 years, is highly unlikely. See http://www.straightdope.com/classics/a5_258.html for more details.
Twotall