Trivia: When Merry and Pippin light the firework, Billy Boyd was so shocked by the firework going off when it was being filmed that he actually let out the high pitched shriek that is heard when the tent goes up. In some of the behind the scenes stuff, Dominic Monaghan makes fun of Billy by calling him 'a slightly feminine character', while poor Billy tries to defend himself.
Trivia: The scream of the Nazgul (Ringwraiths) is actually Fran Walsh, co-writer with Philippa Boyens and Peter Jackson (director) on the film.
Trivia: When the Ring speaks to Aragorn, the subtitles say, "Aragorn, Aragorn, Elessar." However, when listening to the words spoken, it sounds like the Ring says, "Aragorn, Aragorn, bless us." Even on the audio commentary, Elijah Wood (Frodo) says, "I love that the Ring actually speaks to Viggo, as it tempts him, 'bless us', that's amazing, I didn't pick that up until the third time I saw the movie." The other three Hobbit actors (Sean Astin, Dominic Monahan, and Billy Boyd) seemed to concur. (01:17:50)
Trivia: Gil-Galad shows up in the movie during the prologue. He has armor like all the other elves, but he is wearing a blue cloak. He is the one who pins an orc to the ground with a spear.
Trivia: During Bilbo's party, right after Merry and Pippin set off the dragon rocket, we see Pippin's blackened face, then Merry's blackened face, then a shot of four Hobbit guests looking up at the sky, three males and one female - the female Hobbit is on the right side of the screen. I may be completely wrong, but I think she might have been played by Philippa Boyens, one of the movie's screenwriters. There are some shots of Boyens on the behind-the-scenes disc, especially in the feature called "A Passage to Middle Earth," and she and this Hobbit sure look alike to me. (00:17:33)
Trivia: The climactic fight scene was shot in the middle of a heatwave, with temperatures in excess of 100 degrees. Many of the actors playing the Uruk'hais had to be taken off the set with heat exhaustion.
Trivia: When Pippin causes a loud noise with the suit of armor, Gandalf scolds him by saying, 'Fool of a Took! Throw yourself in next time, and rid us of your stupidity.' The insult in the book was even funnier where Pippin threw a rock down a deep shaft which startled everyone and was scolded by Gandalf as follows: 'Fool of a Took! This is a serious journey, not a hobbit walking party. Throw yourself in next time, and we'll be rid of your stupidity. Now be quiet!'
Trivia: Gollum's appearance in this film is different from the other two in the trilogy, as an earlier design was used due to scheduling issues. Partly for this reason he's only seen in brief glimpses. Peter Jackson has joked that he might create a "Special Edition" in the future and fix the discrepancy.
Trivia: Bilbo's birthday cake really had 111 candles on it. The cake was polystyrene, and eventually caught fire because of them.
Trivia: When Bilbo drops the ring, a magnetic ring and floor were used to stop it from bouncing, emphasising its weight and significance.