Revealing mistake: Obvious use of a "green screen" when Elvis and Dylan are sitting on the steps in the stairwell. The five distinct steps that could be seen behind them become a gray wall and the blue handrail posts to the right of the screen become oddly grouped, appearing to be parallel to the right side of Elvis' shoulder/back. (01:09:00 - 01:09:25)
Revealing mistake: When Danny and the others are riding in the "RLC" truck to the bank, the sky is mostly a pale blue (almost white at times), but is suddenly a darker blue between two buildings. After returning to mostly pale blue, the sky turns into a much larger area that is a darker blue, then goes back to pale blue. Suggests filming on different days and/or use of CGI to fill in the sky but failing to use a consistent or similar color. (00:18:25 - 00:18:56)
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: The $100 bills in the briefcase looked quite fake and were obviously a prop. (00:13:40)
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 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: The "rain" moves with Nina, being heavier (or present) on which side of the screen she is on. Then there is no rain on the street when Nina is off-screen, but it is pouring behind her when she gets inside the building. (00:14:35)
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: 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: 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 appearance of the buildings/scenery opposite of FBI Director Gabriel Robinson's office vary, indicating the occasional use of a "green screen." The angles are inconsistent (wider or in the opposite direction) and sometimes grass and/or trees can be seen where the avenue between the buildings should be visible. (00:10:05 - 00:10:38)
Revealing mistake: The size of the spider walking off Sam's face becomes disproportionately smaller too fast compared to its size while on her cheek plus the spider's awkward movements are indicative of CGI. (00:02:20)
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 rhino that killed (or "erased") Paul was obviously CGI and quite fake-looking, especially the way it was running. (01:32:50)
Revealing mistake: The front and rear views of the house did not seem to properly fit together. The rear view showed more sections, making the house longer than what the front indicated and had three high chimneys compared to only one from the front. The rear view also showed several trees that would be aligned in front of the house, but the trees did not appear to be situated that way. (00:27:49 - 00:29:52)
Revealing mistake: When Otto, Tommy and Marisol find the frozen cat outside of the house it is a puppet prop. A few seconds later Tommy is holding it now back to a real animal and is bone dry.
Revealing mistake: An exterior view of the damaged building was shown after Orlando's chair bomb blew through the 10th floor windows. The damage from the earlier explosion on the 4th floor could be seen in the lower left-hand corner. However, there were only two floors between the damaged floors [putting Orlando on the 7th floor] when there should have been five. IF the 4th floor was actually the 4th floor, there were not enough floors above it for the bank to be on the 12th floor. (01:20:44)
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: 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)