Continuity mistake: When Harry wakes up after having his first nightmare the pillow under his head change position in the next shot.
Revealing mistake: During the Yule Ball there is a shot of Professor Moody sitting on a bench tapping time with the music. One can easily see a green object beneath the bench. It is apparent that a hole was cut in the cushion with his real leg hanging below the bench covered with a green leg and foot sleeve. The large green object is his foot with a red dot on his toe. In post production the actor's real leg and foot is to be removed digitally via green screen-like technology and replaced with a digitized artificial one. The red dots are to help coordinate the movements and position of the artificial leg with the actor's real one. This shot obviously got missed by the postproduction team. If you look closely you can also just make out his knee peeking below the fringe of the bench. (01:18:50)
Continuity mistake: When Harry returns from the cemetery, there's a shot of him lying over Cedric's body. When Dumbledore reaches out to put his hands on Harry's face, Harry's left shoulder is higher while he rests his weight on his right arm. The scene cuts to a rear view, and his right shoulder is now higher. When it cuts back to a front view, his left shoulder is once again in the higher position.
Visible crew/equipment: When Harry takes out the licorice snap it cuts him and when he bends down to get one you can see his mic pack. (01:38:50)
Continuity mistake: In the scene where Hermione makes Harry stand up after his name has been retrieved from the Goblet of Fire, Ron continues to look straight ahead and has an emotionless expression for that shot. In the next shot when Harry is walking to Dumbledore, Ron's head is suddenly slightly down and moving up towards Harry, and a glare has appeared on his face.
Continuity mistake: When Cedric puts his name into the Goblet, you can see that his hair is wet on his fringe and stuck to his forehead in several clumps of hair. After he has stepped away from the Goblet, his hair has changed position. The clumps of hair are in different places and a gap has appeared. (00:28:00)
Continuity mistake: When Dumbledore rages on Harry and asks him if he put his name in the Goblet of Fire, he first only put his right hand on Harry's shoulder, but in the next shot his left hand also appears on the other shoulder.
Visible crew/equipment: When Harry is in Moody's office after the third task, and Moody closes the cabinet door after searching for more potion, a crew member in a white shirt is reflected in the cabinet's glass.
Continuity mistake: When Harry is being told by Dumbledore that he's home, Dumbledore's hands change position instantly. (02:05:20)
Continuity mistake: On the Hogwarts Express, Harry's hair changes in level of scruffiness. In particular there is one bit that sticks out to the side on his left that keeps changing. (00:14:30)
Continuity mistake: When Mad-Eye is blasted by Dumbledore he flies back with his hands in the air and hits the wall. Camera cuts and now his arms are down and he hits the wall again. (02:09:45)
Continuity mistake: The numbers on the blackboard in Moody's lesson keep changing. (00:24:00)
Continuity mistake: During the first challenge, the arena/stadium is significantly smaller during the bird's eye view CGI scenes than the physical scene's interior shots.
Continuity mistake: Just after Harry says to Mad-Eye that he never mentioned the graveyard, there is one shot of Harry and his arm isn't cut or bloody. (02:08:20)
Continuity mistake: The way Dumbledore catches Krum's name from the Goblet changes instantly. (00:30:45)
Continuity mistake: When Barty Crouch Sr accuses Harry, Ron and Hermione of casting the Dark Mark, the way he holds his wand changes depending on the angle. (00:12:20)
Continuity mistake: The size of the paper that has Harry's name on is considerably smaller when Dumbledore gives it to Harry. (00:32:20)
Chosen answer: Dumbledore did not know that Voldemort set a trap inside the maze. Unlike the book, there are no magical creatures or riddles to overcome inside the maze. What Dumbledore is referring to is a test of courage. The four champions must overcome their individual fears in order to successfully navigate the maze and win the tournament.
raywest ★