Audio problem: Before the Trade Federation Droid Control Ship starts exploding from the inside, a Neimoidian says, "Nothing can get through our shield". But his mouth doesn't move until after he's said it. (01:57:45)
Audio problem: After Anakin has won the Podrace, he yells, "Mum, I did it! Yeah!", but the words don't quite fit his actual lip movement. (01:07:00)
Audio problem: When Obi-Wan rushes through the Force Doors, after Qui-Gon's death, to face Maul, watch and listen carefully. Obi swings his lightsaber three times in rapid succession, Maul blocks all three attacks. The lightsabers appear to contact, there is even the almost subliminal flash from the beams hitting each other, but the sound crew only inserted two contact sound effects, and those two sounds are slightly out of sync with the actual movements.
Audio problem: When Daultay Dofine says his first line of dialogue which is, "I knew it. They're here to force a settlement.", he speaks with the voice of Rune Haako, the Neimoidian who says, "Have you ever encountered a Jedi knight before, sir?" shortly after. (00:03:35)
Audio problem: When Obi-Wan checks Anakin's midi-chlorian count, he says that he has a count of over "twenty thousand", but the movement of his lips indicates that he's saying "ten thousand". (00:48:45)
Audio problem: On Naboo, when they are planning to take over the palace just after the Queen asks R2 to project the map of the palace - watch her lips, they aren't in sync with what she says. (01:39:20)
Audio problem: After Obi-Wan and Qui-Gon are greeted by TC-14, as they're walking over to the windows, Obi-Wan says, "How do you think the Trade Federation will deal with the Chancellor's demands?" His mouth is visible as he says the last word, and even though he's far away, you can see that his lips are not moving. (00:03:25)
Audio problem: When Anakin is working on his Pod and his friends show up, you hear them laughing. When they leave, if you listen carefully, you can hear that the soundtrack used for laughter when they first showed up is played again. (00:45:50)
Audio problem: When Anakin and Qui-Gon are running to Amidala's ship, Anakin says, "Qui-Gon sir, wait, I'm tired" but his lips hardly move when he says this. (01:13:35)
Audio problem: After the control ship blows up, one of the pilots says, "Look, one of ours out of the main hall." His lips continue to say "way" (as in hallway) but the sound is cut off.
Audio problem: When Obi-Wan and Darth Maul are fighting, after the second time Maul swing his lightsaber over Obi-Wan's head, their lightsabers make contact three times, but there are four clashing sounds. (01:56:35)
Audio problem: Where Natalie Portman and some of the security detail are fighting in the Palace corridors, her shiny weapon makes a distinct noise and the normal blasters makes a different sound. Later, she is given a regular blaster to get up the outside of the Palace. However, when she fires that gun to break the window they've ascended to, it makes the same noise as her shiny blaster, not the sound of a normal blaster. (01:50:31)
Audio problem: When Anakin is working on his pod racer, a group of children walk over. They remark that he will never get it to work. As Seek (Oliver Walpole) says "come on, let's go and play ball", his mouth doesn't seem to line up with the word "ball." (00:48:14)
Audio problem: After Qui-Gon and Obi-Wan enter the hangar bay of the Trade Federation ship, Qui-Gon says, "Battle droids." His face is seen from the side, but you can still see that neither his lips nor his jaw is moving. 0:07:15. (00:07:15)
Audio problem: When Queen Amidala shows the holographic map of the palace and discusses the plan for sneaking into it, you can tell that her explanation of the plan is a recording. There is one shot where you can see her face and her lips are not moving.
Audio problem: When the Viceory and his assistant talk, most of the time their mouths don't match their words.
Audio problem: When the droid army are marching into battle at the end we hear a marching army, but they're walking on grass and the sound should be muffled in some way.
Audio problem: After the transport is destroyed in the hangar (near the beginning of the film) the scene cuts to Obi-Wan and Qui-Gon. The sound of their lightsabers being activated occurs before they even draw them from their belts.
Chosen answer: According to "Inside the Worlds of Star Wars: Episode I" by Kristin Lund, they are "laser doors which lock into position in response to potentially lethal power outputs that occur intermittently during plasma activation process" (the fight takes place in a plasma energy processing plant). There are six laser doors in deference to an ancient Naboo legend in which Chaos is held back by six inpentrable gates. As you say though, they're really just a plot device to add dramatic tension to the duel!
Sierra1 ★