Continuity mistake: Near the beginning of the film, when Frodo and Gandalf are riding in his cart together talking, there are some close-up shots of just one character or the other. However, the background in the Frodo shots and the background in the Gandalf shots are moving at noticeably different speeds.
Revealing mistake: When Saruman and Gandalf are dueling in the tower, Saruman throws Gandalf above a door with his staff. Gandalf is stuck there, but when he falls, the wall moves very slightly.
Continuity mistake: In the opening shot of Bag End, as Bilbo says, "The Third Age of this world," we see the halls outside of Bilbo's study as Bilbo writes. There is a dresser with books on it, books lying near the coat tree, stacks of books and papers all over the floor and against the walls. Later, just before Bilbo says, "Frodo, someone at the door," and then when Bilbo searches for the Ring in the hall, in all three of these shots, the arrangement or even existence of quite a few of those books and papers is different. This has nothing to do with his search of the Ring.
Continuity mistake: After hearing noises out the window, Gandalf tells Frodo to, "Get down," and reaches for his staff leaning on the mantle. In the close-up when he grabs the staff, on the mantle there are books on the left end with a box near it, and a piece of paper leaning up against the wall between the two. In the wide shot just before this shot, there is no paper between the books and box. Also, the paper lying between the books changes from previous shots and when he starts heading for the window, behind him on the mantle the paper to the right of the candlestick changes position in the following shots.
Continuity mistake: When Gandalf and Bilbo are outside Bag End we see the cloth topped table against the wall that has papers, packages and a candelabra on it. In the shots from outside, the table end closest to the front door is located right under the second decorative beam of wood on the wall, away from the inside archway. In the indoor shot when Gandalf and Bilbo come in, the table end is located right at the archway.
Continuity mistake: Frodo is in the kitchen packing apples and other food for his journey to Bree. Frodo asks Gandalf, "And the Ring will be safe there?" Behind Frodo, to his right, the window and table in the next room are seen. The chair near the table, is not the same chair that is next to that table in all the rest of the shots of the area. The window is shut, but when Gandalf and Frodo are soon in there it is open when Sam isn't "dropping no eaves." It cannot be assumed that Sam would have opened the window. The existence and arrangement of books and papers on the window bench also differs.
Continuity mistake: The Troll hasn't even entered the doorway yet, and both Sam and Aragorn look way up, as if the Troll were standing right in front of them already, but the Troll is only visible more in the distance, through the door. Since the Troll is still only in the doorway for them to see, the eye angle should still be towards the doorway, not up over them. Then when the Troll smashes through the doorway, and walks towards Sam, in the same shot as earlier, Sam looks way up at the Troll, but this time the eye angle is correct.
Continuity mistake: While Gandalf is nervously waiting, Frodo is looking for the envelope with the Ring in the wood chest. In the first shot looking up from the POV of the chest, Frodo holds the envelope with the flap up near his fingers and the seal below it. However in the next shot the envelope is reversed, with the flap opposite his fingers.
Continuity mistake: During the prologue, after Sauron strikes Elendil, we see Narsil falling right at the corner of a dirtless, sandless smooth rockface and the sword has only some blood stains on it. When Isildur grabs Narsil, it is now in the middle of dirty, sandy rock, and the sword has dirt all over it now.
Deliberate mistake: There is a shot of the Fellowship in Moria running towards camera as the entrance collapses behind them, in this shot you can see that the hobbits are obviously not Elijah, Sean etc. but their scale doubles.
Continuity mistake: At Bag End, when invisible Bilbo reappears in the hallway, we see books on the shelf of the coat tree. As Bilbo leaves Bag End, he opens the front door, again we see books on the shelf of the coat tree. In both of these shots, the amount and arrangement of books differ.
Continuity mistake: When Arwen is being chased on horseback through the woods by the Ringwraiths, at one point her face gets grazed by a tree branch, which leaves a long red scratch on her right cheek. In the following shot from up behind the horse she's riding, when she turns around one more time to see where the Wraiths are, her face is conspicuously unblemished, only to have the scratch re"surfaced" on subsequent close-ups. Also, during this long flight to the Ford sequence it is quite discernible in many cuts by cueing on her face (esp'ly in slo-mo) that the rider is a stunt double.
Continuity mistake: When the Cave Troll stabs Frodo, and then you see Sam close up and yelling "Frodo" He has 2 bloody cuts on his left cheek, and near his lip. But when the Troll is killed, and he slowly approaches Frodo, the cuts are moved further back, so they aren't as noticeable. But when Gandalf 'dies', and you can see Sam close up again, crying, the cuts have vanished all together. (The second timecode is when the cut vanishes all together).
Revealing mistake: After Boromir is shot twice, he turns around and kills one Uruk Hai, and then when he kills the second one, you can see the sword wiggle after he slices the enemy's legs.
Continuity mistake: When Aragorn is kneeling with the dying Boromir, the amount of blood on Aragorn's mouth/nose slowly decreases throughout the scene, though he never wipes his face.
Continuity mistake: When Gandalf comes to Minas Tirith, the river is noticeably closer to the city than it is in "Return of the King."