Directed by: Brian De Palma
Starring: Tom Cruise, Jon Voight, Ving Rhames, Jean Reno, Kristin Scott Thomas, Vanessa Redgrave, Henry Czerny, Emmanuelle Béart
Revealing mistake: When Ethan uses the magnetic screwdriver to undo the screws holding the grille to the air-vent in the NOC list room, the spindle that is actually turning the screw is visible after it falls out.
Revealing mistake: When we see a close-up of a knife being pulled out of a man's stomach, it's obviously a prop knife where the blade goes into the handle, as we can see the end of the blade while it's being pulled out. (01:19:50)
Factual error: The vents that Hunt and his sidekick crawl down at CIA Headquarters are standard galvanized steel box vents; they are very common in the building trade. Try walking or crawling down one - you'll make a noise like the sky is falling down. People will be able to hear you for miles. Every person in that building would know somebody was crawling about in the vent system. (This error applies to dozens of films, not only this one.)
Trivia: An early draft of the script was set to feature several characters from the original series all being killed off to raise the stakes for the new characters. The producers wanted to bring back as many of the original actors as possible. All declined, as they felt it was disrespectful to the original series. As a result, only the character of Jim Phelps was brought back, albeit as a surprise villain and not a hero.
Question: Did Ethan actually know it was a mole hunt to trap Jim, or was he oblivious until he worked it out at the train station?
Answer: Ethan never thought it was a mole hunt to trap Jim. He found out from Kittridge at the restaurant that it was a mole hunt, but Kittridge believes that Ethan is the mole (the money his parents mysteriously receive). At the station Ethan realises that Jim must be the mole since it is too convenient both he and his wife survived. However, the hunt to catch the mole was never directed at Jim - Kittridge never suspected him until at the end when he sees Jim alive.
Actually had suspicions before Jim showed up. Ethan found the Bible that was stamped from the Drake Hotel. Where Jim had literally just come back from before the mission. It made no sense otherwise why that would be in Jim's possession.
Suggested correction: "People will be able to hear you for miles. Every person in that building would know somebody crawling about in the vent system." No, they won't. The sound from someone crawling through a vent would carry for metres but not miles. CIA Headquarters are quite large, so it's unlikely that the sound would carry to every part of it. And even if it did, there's no reason to believe that every person in the building would know that the sound was somebody crawling about in the vent system.
The galvanised steel the box vents are made out of makes a very distinctive booming sound when it distorts under pressure, and it is loud. Unless they are deaf, the people in the room through which the vent runs would know perfectly well that there was someone in there.