Audio problem: In the scene after Norman goes for a late-night swim, when he's telling Maureen that he slipped in the mud, you can see that his mouth never moves, yet he speaks the words "I slipped in the mud."
Audio problem: Right before Charley gets thrown into the closet doors, Jerry has him by the throat threatening to kill his mother if she wakes up. In the shots of Charley trying to free himself of the grip, Jerry's lips are moving but no sound can be heard. (00:28:15)
Audio problem: When the Geckos shoot Chet Pussy, the sounds of gunfire don't match the visible gunshots. (01:00:25)
Audio problem: In the scene where Rose is talking to the demonic form of Alessa, watch her mouth as she says "Christabella will find Sharon." Alessa's mouth doesn't match every word she says.
Audio problem: Nancy shouts, "Yay Chris! Go long! Go for the pass, baby!" at football practice, and her voice is so distorted that the viewer can easily tell the line was added post-production (with too much gain).
Audio problem: This problem exists in the extended Director's Cut. When Narcisse is first introduced in the hospital, when we cut outside to Decker and the police walking to the room, they suddenly hear Narcisse grunting which makes them rush to his room. However, they are quite the distance from his room, and Narcisse's grunts are fairly low, so it's obvious they shouldn't have heard him from that distance. The audio mixing tries to make his grunts sound louder, but it doesn't sound right at all... they're way down the hall from the room, but his low grunts sound like they're coming directly right next to them. This is all the more confusing, as in the theatrical edition, they are alerted to a distant scream by a nurse, which was much more believable. (As the Director's Cut is currently the most readily-available version of the film on Blu-Ray online, and is the director's intended edition, I believe it should count as a mistake).
Audio problem: When we see a close up of the LP playing on the gramophone, you can occasionally see the needle is not actually touching the LP but sound is still heard.
Audio problem: In the scenes inside to cabin where Angela keeps her victims you can hear flies, but there are no visible flies anywhere.
Audio problem: When the unnamed Asian man sells Frank the box at the beginning, watch when he says the line "it always was." The words don't quite match the lip movements, revealing the line was looped in post.
Audio problem: When Susan's cutting the cake in the kitchen she drops the plates upon discovering David's body yet there's no sound of them breaking. (00:04:25)
Audio problem: When Patrick Bateman is exercising and watching The Texas Chainsaw Massacre, the audio does not match up with the actual film. (00:37:05)
Audio problem: When Frank says "Stay away from it!" whilst trying to shoot the truck during the chase sequence towards the end of the film, his mouth doesn't move.
Audio problem: Eddie Brock is trying to find where Carnage might be headed. To draw inspiration he listens to the recording of the last time they spoke (when incidentally he was never seen retrieving the tape). However, the lines in the recording are different takes from the original scene, spoken at a brisker pace without dramatic acting pauses. (00:38:00 - 00:42:40)
Audio problem: Just after Quinn has been nailed to the wall at the beginning of the movie, he makes some strange noises and then starts talking in "vampire language." This has obviously been dubbed in post-production.
Audio problem: Throughout the entire film, much of the audio is inaudible, and in several key scenes (including most scenes set in cars), you can hear a loud sort-of "crunchy" and windy sound from the microphone.
Audio problem: At the beginning of the movie, a local errand guy delivers a box to Poirot from a gondola. The actor is supposed to be speaking Italian in his first phrase, but he says "Segnor Poirot, lo pesce!" (Mr. Poirot, your fish!), totally off in accent and grammar, obviously from an English-speaking actor poorly faking an Italian accent. Moreover, the box does not contain fish, but turns out a few minutes later to be a box of chocolates. In fact, the Italian version redubs this line entirely and the guy says the equivalent of "Mr. Poirot, your sweets" in a Venetian accent ("Sior Poirot, I suoi dolcetti!").
Audio problem: When Nada first sees the police helicopter, the only sound is a very muted whooshing of the blades. Any other time, the noises are normal.
Audio problem: When Richard is running around the house trying to find Jen near the end, he is heard ferociously breathing and grunting. The breaths and grunts appear to have been dubbed in as Richard's facial and chest movements remain mostly still, which wouldn't happen if he was breathing and grunting that heavily. (01:41:10)
Audio problem: When Oggie races the Turbo interceptor, the engine sounds for his car are from a V8, though his Chrysler Daytona is powered by a turbocharged 4-cylinder.
Audio problem: At the end when the killer falls through the floor, he screams. However, you can see that his mouth does not move.