Acting for Two: Lawrence Makoare has a scene between himself as Gothmog and himself as the Witch-King. Additionally, Gothmog's voice actor, Craig Parker, also voices the Orc commander's subordinate, Guritz.
Christopher Lee helped direct his death scene, since he knew from his World War II service how people react when getting stabbed in the back.
King Theoden touching the spears of his soldiers before they charge into battle was Bernard Hill's idea.
Awesome, Dear Boy: Invoked—Peter Jackson insisted that only riders who had read and enjoyed the books were placed at the front for the epic cavalry charge. This was to ensure that the riders fully appreciated the significance of the moment and fully bought into it. From some of the shots of the riders charging gung-ho into the fray, this little touch worked beautifully.
Author Phobia: Peter Jackson actually used his own phobia of spiders to measure the effectiveness of Shelob's design and animations. By all accounts, it worked.
Cast the Expert: The New Zealand Army provided extras for the final battle in front of the Black Gate. Behind the scenes commentary on the DVDs makes note of how good they were at following directions and setting up formations, as well as how much enthusiasm they brought to the combat scenes.
Billy Boyd's singing scene largely came about because co-writer Philippa Boyens went for a night out at a karaoke bar with the younger male cast members, and she was very struck by the quality of his voice. Remembering that Denethor asks Pippin to sing him a song when Faramir heads off to war, she resurrected the lyrics from the novel; where it is actually sung by all four hobbits in the Fellowship of the Ring, and Boyd came up with the tune for it.
Viggo Mortensen also composed the tune and sang the part to the song Aragorn sings at his coronation. The translation of the Elvish words runs "Out of the Great Sea to Middle Earth I am come. In this place I will abide, and my heirs, unto the ending of the world." This is, according to the book, the same verse Elendil sang when he first arrived in Middle-earth from Númenor.
Christopher Lee was understandably not happy that his one (and only) big scene was cut from the theatrical cut (if he had been kept he would've got a SAG Award for Best Ensemble Cast). But he eventually reconciled his feud with Peter Jackson to be in The Hobbit.
The role of the Cavalry of the Dead is considered by Jackson to be this due to its Story-Breaker Power and "being unbelievable". If it had appeared any earlier, the Siege of Minas Tirith would have been one-sided and the Ride of the Rohirrim would have been unnecessary.
Crosscast Role: Most of the Rohirrim riders were played by women. It's less obvious thanks to the helmets and fake beards.
Deleted Scene: A wedding scene between Faramir and Eowyn was shot but wasn't used in either the theatrical or extended cuts of the movie. Miranda Otto eventually posted a photograph of her and David Wenham in their costumes from the scene.
Directed by Cast Member: Peter Jackson allowed Andy Serkis to direct the Sméagol flashback scenes. He was so pleased with the result that Serkis was made 2nd Unit Director when they returned to make The Hobbit trilogy, which launched Serkis' directorial career.
Seen in several trailers but cut is Merry pledging his sword to Théoden. The scene finally appears in the extended edition.
The scene of Éomer cradling Éowyn's unconscious body didn't appear in the theatrical cut, but was restored for the Extended Edition.
Never Work with Children or Animals: When filming the scene "The Sacrifice of Faramir", David Wenham's horse became excited and ran away with him. A professional rider had to chase the horse and stop it. David was not a rider, and had not been taught what to do in such a situation, to pull the rein and force the horse to turn too sharply. Horses cannot run in a tight circle, and this would have stopped the horse. Thankfully, David was not harmed.
One-Take Wonder: The "oil" that Denethor pours over himself and Faramir was a combination of water and glycerin, to achieve an appropriate glistening effect. Because this soaked the wigs and costumes, this scene had to be filmed in a single take.
Orphaned Reference: King Théoden orders Grimbold to take his company right, "after you pass the wall". The line is taken straight from the novel, and the wall he's referring to is the Rammas Echor, a large wall encircling Minas Tirith and the Pelennor Fields, which the Orcs of Mordor breached on the way to the city. However, the wall itself doesn't appear in the movie, which may leave some viewers confused or thinking he was referring to the outer wall of Minas Tirith itself.
Real-Life Relative: Sean Astin's eldest daughter Alexandria, who was 4 at the time, played Sam's daughter Elanor in the ending. In the same scene Sarah McLeod, who plays Rosie, is seen holding a baby played by her infant daughter Maisy.
Spared by the Cut: The theatrical cut leaves out Saruman and Gríma's appearance, leaving them effectively imprisoned in Orthanc. The extended edition restores the scene, in which Gríma kills Saruman before being killed by Legolas. Their deaths here confirmed that the Scouring of the Shire epilogue in the book would not be adapted. Gothmog's death during the Battle of the Pelennor Fields is also omitted from the theatrical cut; he's last seen backing away from the Rohirrim charge.
John Rhys-Davies ad-libbed the line "Here's to dwarves that go swimmin' with little hairy women!"
The "rat catcher's cottage" in Minas Tirith. The build team interpreted one of Alan Lee's drawings of a building as having a dead rat hanging in the window, and based an entire house around the idea that the Official Gondorian Rat Catcher lived there. Alan Lee maintains he didn't have something so specific in mind when he did the sketch, but then he realized that it was completely logical: after all, a medieval city the size of Minas Tirith would have a rat problem.
Troubled Production: Post-production for this movie took much longer than expected.
While editing the film, Jackson kept requesting more effects shots, more troops added to Pelennor Fields, and more live-action plates of Rohirrim on horseback.
Gollum's death scene took more development time than any other shot, and the final result still looks a bit janky (there aren't any flames rising up around his body when he goes into the lava, unlike, for example, the T-800 submerging into the molten steel at the end of Terminator 2: Judgment Day.)
Philippa Boyens says there wasn't enough time to relieve the sense of Ending Fatigue by reworking the script so that it didn't have so many fake-out endings.
The final print of the film wasn't delivered until the day before it premiered. At the premiere, Jackson admitted that this would be the first time he had a chance to watch the whole movie from start to finish.
Wag the Director: Eomer wasn't supposed to be with Eowyn when Aragorn came to heal her, but Karl Urban fought for it, arguing that he would not leave his sister's side until he knew she was alright.
What Could Have Been: There were more than a few ideas for the final battle that were filmed but ended up being cut or edited over by the time of the release.
When the Black Gates open, Aragorn seems to be entranced by the light of the Eye, which calls out to him. Originally this was meant to be the angelic form of Sauron.
In addition, filming was done of Aragorn fighting Sauron in his armor in the battle, but when the decision was made to edit this out, they digitally edited a troll over Sauron's armor, but there are still a few places where Sauron's armor can be seen because they didn't quite cover it all up.
of her and David Wenham in their costumes from the scene.