Revealing mistake: There's something odd about the chair that is (or is not?) to the right of Monsignor Kelly when Stu goes into his office to talk. Only part of the back of the chair can be seen and it is not directly in front of the Monsignor, but there is not enough room for the seat part to be there (otherwise, the Monsignor could not be standing where he is). Without any indication that the Monsignor or chair moved, the Monsignor is later able to rest his right hand on the chair's back. (01:13:57 - 01:14:37)
Revealing mistake: Corporal Shah is tied and on a chair in the command center. He then receives a powerful blow to his left check, knocking him sideways and rendering him unconscious. But his glasses do not even move a millimeter.
Revealing mistake: The French tanks that attack Paul et al. Towards the end of the second act are supposed to be Saint Chamond tanks. There is only one of those left in the world, and it is not on screen: the undercarriage and tracks don't even come close to looking like that of a Saint Chamond, because it's actually a BMP-1 dressed up to look like a Saint Chamond.
Revealing mistake: Jimmy's [Matthew Lawrence] glass of cola on the table is filled to a level slightly above the groove (mortar joint) in the cement block wall. The next front view shows the top of Jimmy's glass slightly above the same groove and the level of cola is about 2" below the groove. A little later, the level of cola in the glass is like it was earlier - slightly above the groove. A cement block wall is stationary and nobody raised or lowered the table; use of a green screen can explain the anomaly. (00:08:05 - 00:08:41)
Revealing mistake: The owl that JP saw was obviously "fake" (stuffed or CGI). Its nose was crooked and its puffy cheeks made it look like it had cheek filler injections; owls have flat faces. (00:32:50)
Revealing mistake: The cell bars appear to be about 4" apart, but are much wider to accommodate the width of The Artist's face/head when there's a close-up of him next to the bars. (01:13:50 - 01:15:09)
Revealing mistake: The chalet was visible behind Emily when she was outside talking on the phone, but subsequent views of Emily showed her in front of a solid white background (mimicking snow) - indicating the use of a green (white?) screen. (00:13:34 - 00:13:56)
Revealing mistake: Younger Tom dropped his policeman's jacket onto the "fire" and when Younger Marion came over to the fire (almost 30 seconds later), the jacket still had not caught on fire. The next time the jacket was shown, most of it still looked unscathed by the fire. (01:33:30 - 01:35:36)
Revealing mistake: The guy with the sunglasses changes from behind and in front of shots. (00:09:46 - 00:10:15)
Revealing mistake: Driving home from meeting Gigi, there is an image on the windshield of a blue handicapped parking permit/placard that is supposed to be hung on the rearview mirror, but there is no placard hanging - the permit's image is superimposed on the windshield. The image even briefly appears and reappears. (00:34:05)
Revealing mistake: The stairs are a prop. About a dozen steep steps - just to the landing - are almost as high as the front door. (00:55:48)
Revealing mistake: When William and Jack open the door, enter the room, and walk past the helium-filled balloons (tied to a chair about 4' away), the balloons remain immobile. Due to how light helium balloons are, just opening the door or breathing nearby would be enough to cause the balloons to move somewhat - if they were actually there. (00:16:00)
Revealing mistake: In the scene wherein Detective Marquez and Senora Borden are drinking wine by the (indoor) pool, the back of Det. Marquez's head is disproportionately large. Front views of Det. Marquez often show his head tilted to the left, but rear views usually do not and his head might even be tilted to the right. Also, Senora Borden's eyes do not appear to be aimed correctly at Det. Marquez's (especially since they are facing each other with heads tilted to the right). Use of stand-in and/or green screen. (01:02:30 - 01:03:10)
Revealing mistake: A white truck could be seen in Tamra's rear window, following her car at varying distances. After Tamra hit Randall on his bike, the white truck was still there but gone when the camera returned to a front view of Tamra. Use of a green screen - the truck could not have gone past the accident or "disappeared." (00:03:35 - 00:04:10)
Revealing mistake: Dave Bautista announces that he has arrived. There's a close-up of the kickstand, and you can actually see scratches on the asphalt from previous takes (spotted also by Rian Johnson himself in his video breakdown of the arrival scene for the Vanity Fair youtube channel). (00:15:10)
Revealing mistake: The "snow" that Kip and his friends jumped into after leaving the bath house was obviously fake (like the "snow" on the pine trees). Beads of "snow" do not fly into the air when impacted by a weighted object, such as a body. (00:22:32)
Revealing mistake: There are noticeable differences in the appearance/condition of the lattice panels on the deck (overlapping; whether there are missing/broken slats and, if so, their locations), but pinpointing most of the differences would require pausing. When Thomas was seated in front of the panel adjacent to the door, sometimes there were broken/missing slats but other times they were intact. Most revealing was the absence of the lattice panel opposite the front door when Liz was standing near Thomas. (00:42:17 - 00:49:42)
Revealing mistake: When Danny follows Maria outside, he is in front of a well-lighted wide patio door with side windows and there are numerous decorative lights to his right. Thereafter, close-up views of him talking show only some small red lights to his right; the rest of the screen is black. Wide views continue showing the lit entryway behind him. (00:08:44)
Revealing mistake: In the underwater view of the fish, the ice hole is almost perfectly round and the ice appears to be quite thin - nowhere near the several inches Jason and Ben have to chip away to reach water. (00:33:55)