Revealing mistake: As the Uruk-hai are slamming into the chamber door, with the battering ram, Gimli and Legolas are standing at the door. Across the room, Aragorn says, "Ride out with me," then in the next three shots of Theoden, he's standing in front of the same wall, with particular markings. In the very next shot, Gimli says, "The sun is rising," and he's standing right in front of the very same wall that Theoden is standing right in front of. Then, in the next shot, still standing at that wall, Theoden says, "Yes. Yes. The Horn of Helm Hammerhand..." Both Theoden and Gimli, can not be in front of the same wall at the same time. In the next shot of Gimli, still standing at that same wall, responds, "Yes." He then starts to go off to blow the Horn. The next shot, is a close-up of the door - all the men in front of it and some wood are knocked away, due to the force of the battering ram. In the next shot, as Theoden says, "Let this be the hour when we draw swords..." between Aragorn and Theoden, the men are seen huddled together at the door again, and Legolas and Gimli are there too. Yet, in the next shot, Gimli is hurriedly running up the steps of the tower to the Horn. (01:27:20)
Revealing mistake: When the riders break out of Helm's Deep, you can see the hooves on some of the horses pass straight through the Uruk-hai corpses on the bridge. (01:29:10)
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, even though the scene is played at normal speed. (01:29:10)
Revealing mistake: Éomer yells, "To the King!" at Helm's Deep and the Rohirrim begin to ride down, towards the Uruk-hai. In the very first wide shot of Gandalf, starting to lead them down, there is a clear reflection of three of the riders and their horses, shown on the ground. (01:29:55)
Revealing mistake: During the destruction at Isengard, Treebeard says, "Break the dam. Release the river." While he says that, there is a close-up of the dam wall as the Ent pulls away the wood blockades. We see the water starting to spurt between certain stones. Then there is a wide shot of the area, and in this shot, the water does not start to spurt between the same stones or in the same manner as in the previous close-up. (01:31:50)
Revealing mistake: In Osgiliath, when Sam and Frodo are falling down the stone steps, both of their knee pads are revealed because their knickers ride up at the knees during their fall. (01:34:15)
Revealing mistake: When Sam and Frodo are talking after Sam called Gollum "Stinker," you can see, in some of the shots, Sean Astin's brown hair under the golden wig. (01:37:00)
Revealing mistake: When Gollum brings the two rabbits, he drops them onto Frodo's lap, and Frodo is leaning up against one of the broken stone structures. After Frodo opens his eyes, the stone structure behind him vibrates when he moves a couple of times. This structure should be way too heavy to jiggle when Frodo moves. (01:41:05)
Revealing mistake: Sam says "There's only one way to eat a brace of coneys" and in the next close-up, Sam stirs the stew. The rolled up blanket is behind the hanging pot, which means it's on Sam's right. In the next three shots, Sam's pack is behind the pot, not the rolled blanket, to Sam's right. Then, in the next close-up of the pot, it's the very same close-up shot as before, only it's been flipped, and the rolled blanket is there, near the pot again, this time to Sam's left. (01:41:40)
Revealing mistake: Frodo, Sam, Faramir and Gollum are at the sewer in Osgiliath when Faramir asks, "Cirith Ungol?" and then grabs Gollum's neck. Frodo and Sam watch as Gollum is grabbed, but their eyes do not follow Gollum as Faramir grabs him, their eyes remain focused on the ground to their left. The shot of Faramir and the shot of Frodo and Sam were edited together, with Gollum added later. (01:42:20)
Revealing mistake: When Gandalf, Aragorn, Theoden, Legolas and Gimli all ride up the hill on horses towards the end, there is a man on a horse on the left of the screen. Who is he and why is he there? He's Éomer's body double (Karl Urban was unavailable) and at some stage they were going to put Éomer's head on him digitally, but they never got around to it. Director's commentary, extended DVD. (01:43:05)
Revealing mistake: Shadowfax, the horse that only Gandalf is supposed to be able to ride, will not take a saddle and bridle, so throughout the majority of the film, they try very hard to hide the saddle that Gandalf is obviously sitting on, even though you can see him holding the front of it underneath his robes, and sometimes, you can see him holding a very thin bridle. But right at the end of the film, when you have the shot of Gandalf, Aragorn, Legolas, Gimli, etc. on horseback, you see Gandalf's feet in stirrups. (01:44:05)
Revealing mistake: In the shot after Gimli shouts "Send them to me" at Helm's Deep, you see the elf closest to the camera fire an arrow. As he reloads, his right forearm passes though the bowstring. (02:09:05)
Revealing mistake: When the women and children are evacuated to the Glittering Caves under/behind Helm's Deep, in the first shot, a hooded person leans on a stalactite making it sway back and forth. (02:42:00)
Revealing mistake: When the men are retreating into the halls of Helm's Deep, you can see an archer in the bottom right corner repeatedly shooting his bow without an arrow on the string.
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.
Revealing mistake: Just as Theoden yells, "They have broken through, the castle is breached." Legolas is first seen on the exterior wall pulling the string of his bow with no arrow in his hand twice, but the other times he pulls the string on the bow we do see the arrow before reaching the bridge. Also, after he crosses the bridge, before he gets to the stairs, when he reaches behind him for an arrow the arrow is on his back, not in the quiver, it's just simply on his back.
Revealing mistake: In the final shot of Gandalf and the Balrog's plunge into the underground lake, a seemingly solid rock in the top-right hand corner disappears for a moment, leaving a black void.
Revealing mistake: The scene at the top of Saruman's tower when he is looking down watching the Ents is shown in reverse. His hair is the giveaway, blowing the wrong way. After cutting away to the Ents once more, they reversed the film again, when he is walking backwards.
Revealing mistake: When the camera moves into the "Seeing Stone" and pans up to reveal "the great eye," the entire tower was a miniature. It's not that noticeable, but what really makes it a mistake is the cotton balls used to make smoke on the smaller towers leading up to the big one. (It sticks out so obviously that one must ask, why did they CG the orcs at the bottom of the miniature, but use cotton balls for the smoke instead of CGing it?)
Answer: The movie makes it clear that Gandalf has lost some of his memory and his personality has changed. Gandalf actually did die and pass over to the "other side", as it were but was sent back to complete his task. However, he was sent back as a similar, but different entity. Gandalf the White does not have all the memories of Gandalf the Grey, at least at first. He doesn't even remember that he used to be called Gandalf the Grey until someone points this out to him. It is implied that Gandalf doesn't even remember Sam until Aragorn mentions him. Gandalf then searches his memories and remembers who Sam is and his eventual importance to Frodo's quest. When he finally remembers this, he is pleased that Sam went with Frodo, as he will play a crucial role near the end of the journey.