Continuity mistake: Merry's shirt is untucked under the front bottom of his vest when Pippin chases him and then as he sits on the roots of the tree. The tree starts to devour them. Just after the shot of hairy Hobbit toes, there is a close-up of Merry's jacket and vest, before panning to his face. It shows that his shirt is now tucked in, as well as in the far shot later, when Treebeard rescues them.
Continuity mistake: Sam helps Frodo up and says, "There's some good in this world," then Faramir walks over and the Hobbits face him. Sam's rolled blanket is seen high up on his back, above his shoulders. Yet in the very next close-up, which is a flipped shot, the blanket is way down on his back, way below his shoulders. Frodo's hair is completely different in both shots too.
Continuity mistake: When Legolas, Gimli and Aragorn are standing atop the wall and Legolas says, "Your friends are with you Aragorn," in this close-up we can see that Legolas' right braid is loose and half undone. As Legolas lets loose his first arrow in the rain, his right braid is perfect again. Various close-ups were done in pickups long after the principal photography.
Continuity mistake: Just before Brego comes up to an unconscious Aragorn, his sword is lying on his left side, perpendicular to his body, with the blade facing towards his back and the hilt facing his front. In the next shot, BEFORE Aragorn even rolls over onto his back, the blade is now pointing up his back and the hilt is at his thigh. Also once again, the tear in the coat and shirt at Aragorn's left shoulder is very different in both shots, as it is in many of the following shots too.
Continuity mistake: After Legolas leaps onto Arod, the men on horseback change in their arrangement, as they charge towards the Warg Riders. In one shot Gamling is just drawing his sword, while riding between Theoden and Legolas. Next shot is a Rohan rider directly behind Legolas. Then in the next shot of Theoden, it shows Gamling drawing his sword again, riding behind Legolas.
Continuity mistake: In the first shot of the Uruk-hai running away fom Helm's Deep, towards the trees, the shot of Helm's Deep in the background is correct. The Causeway is littered with many bodies and the ladders are leaning against the Keep and the Deeping Wall with the break in it. However, in the next shot of them, as they are entering the forest of trees with Helm's Deep behind them, the Causeway has no bodies on it and there are no ladders leaning against the Keep. Also visible when Theoden is shouting, "Victory, we have victory."
Revealing mistake: When Theoden, Aragorn, Legolas and the Rohirrim soldiers ride out to meet the enemy just before Gandalf's return, they charge down the ramp into the stampeding Uruk-hai. If you watch the Uruk-hai very carefully you can see that some are running in slow motion.
Continuity mistake: Just after Haldir dies, Aragorn jumps onto a ladder and rides it into a crowd of Uruk-hai. In the close up shot when he first jumps he has his sword in his right hand, but when they cut to a longer shot for the fall his hands are empty. When he lands on the ground, the sword is back in his hand.
Factual error: At the very end of the film, where Sam, Frodo and Gollum are approaching Mordor after leaving Osgiliath, it pans up over the mountains to reveal Orodruin (Mt. Doom) in the foreground to the right and Barad-Dur in the background to the left. According to Tolkien's maps, as seen in the prologue to the Fellowship of the Ring, if they were approaching Minas Morgul from Osgiliath, Orodruin would be to the left and Barad-Dur to the right.
Continuity mistake: At the destruction of Isengard, the dam is broken and the river is starting to break through the wall. In the wide shot as the river starts to break through, we see the wall breaking and all the CG Orcs at the top of the wall falling. In the next close-up, we see the CG Orcs still standing on top of the wall and when they do fall in this close-up, they fall very differently than in the previous wide shot.
Continuity mistake: Aragorn remembers what Gandalf said, "...at dawn look to the East." Theoden crosses the floor in front of Aragorn saying, "The horn of Helm Hammerhand shall sound in the Deep," as Aragorn turns around towards Theoden. Theoden now turns to face Aragorn, as he continues, "one last time." In the next shot, Theoden puts his hand on Aragorn's shoulder, behind Aragorn is a chair to his right. The next shot of Theoden close up shows his back to the front guarded door of the chamber with the chair overturned behind him. Earlier when Theoden crosses the floor past Aragorn, their positions changed. It should be Aragorn's back facing the front guarded door of the chamber now. Also, the overturned chair should be upright.
Continuity mistake: First a shot of the Uruks shooting up the second anchor to the Keep, then there's a shot of a line of Uruks pulling on the cable. In the next shot, an Uruk has his arm wrapped around the frame, between the rungs of the ladder. We can also see the feet of another Uruk, standing on the horizontal ladder. This 'real' ladder has a much narrower width than the CG ladder, we see going up in the next shot, which is wide enough to hold 3-4 Uruks, side by side, as it's being raised to the Keep. Then when it reaches the top of the Keep, it's the 'real' ladder again. There is a VERY noticeable difference between the real ladders and the WETA CG ladders, top or bottom.
Deliberate mistake: When Aragorn, Gimli and Legolas stand and then enter Fangorn, there are multiple shots that are flipped and then not, back and forth. For example, when they get ready to fight the White Wizard, the shots are flipped. The quivers and brooches of Aragorn and Legolas, are the wrong way.
Revealing mistake: When the Ents are releasing the river, on the bottom left hand side, you can see an Orc chopping at an Ent. However, when the Ent moves, the Orc is still chopping the same place.
Continuity mistake: After Legolas yells, "A scout!" Aragorn runs back towards the Rohirrim to warn them. In the first shot, he's running down the hill, straight ahead of him, is Theoden on his horse, Éowyn leading two horses on foot and people to her left. In the next shot, Éowyn's two horses are pointed to her right, there aren't any people to her left, and now standing between Theoden and Éowyn is Gimli with Arod.
Continuity mistake: At Edoras, after the first close-up shot of Éowyn kneeling at the bedside of Theodred, there is a front wide shot. In that shot the animal skin rugs going around the bed differ in position from the next wide shot behind Éowyn. Note especially, the rugs at the foot of the bed on the opposite side of Éowyn.
Continuity mistake: In the opening shot of the stable scene, there is a saddle in the stall next to Brego. A few shots later, you see a man lifting that saddle and start to walk away. There is no saddle in the next few shots. Then the saddle is back again, for Éowyn to pick up. (Extended DVD.)
Continuity mistake: At Henneth Annun, Frodo and Sam have their blindfolds removed, and in this wide shot, behind them to their right one of the Rangers throws a cloth onto a crate that has objects lying on it, and sits down on the sack. In the semi close-up shots of Frodo and Sam, the cloth the Ranger threw lies differently and the things lying on the crate are different too. No one touched them.
Deliberate mistake: During the Warg battle, the fourth shot after the close-up of Legolas letting loose the arrow while riding on Arod, a Warg and rider attack a Rohan. In the background is a particular hillside with some dead bodies, and on the left of the screen lies a dead horse with an arrow in its rear. The very next shot, a horse and rider fall and a Warg attacks the rider. The background hillside in this shot, dead horse and all, is the same background plate as the previous one, only it's been flipped.
Continuity mistake: Frodo, Sam and Gollum are resting in the middle of the Dead Marshes. In the wide shot, Sam gives Frodo some Lembas and takes a piece for himself. Sam breaks his apart and smells it a couple of times, while looking at Gollum he holds the Lembas away from his face. Next there's a close-up of Sam holding the Lembas right near his mouth. The piece of Lembas is much bigger in this close-up, than in the very next shot, showing Frodo and Sam.