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: 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: Max rolled down the front passenger side window and no wind came into the car, but when he had his face barely out the window, his hat blew off (not shown on screen). If wind hit the visor part of his "bugout" hat, the hat would have most likely blown off into the car. (00:03:40)
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 boat's motor/engine was in the center-rear when Annie and Jodie brought it to the beach, but when Nic and the others were looking at the boat, the motor was off to the side (near the corner). The position of the motor varied, sometimes being in the corner when one of the riders would have obstructed its view. The appearance of the motor and which direction it was facing, the size of the tiller handle, and whether the water inlet port/propeller could be seen also varied. (00:48:57 - 00:49:47)
Revealing mistake: During the struggle in the elevator, the pistol discharged three times into the ceiling (covered light) but no fragments fell. A little later when the whole ceiling is shown, the ceiling is not damaged and there aren't any signs of bullet holes. (01:04:35 - 01:05:12)
Revealing mistake: The $100 bills in the briefcase looked quite fake and were obviously a prop. (00:13:40)
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: Robert's upper body is leaning against a pillow with his adjustable bed at about a 60° angle, and stays at this angle when there are front views of him. After Paul arrives, views of Paul that include only part of Robert's stomach/torso show Robert lying at a lower angle, closer to 45°. Sometimes, the blanket representing where Robert's stomach would be is all that is included. Robert [Bruce Willis] probably was not present when front views of Paul were filmed. (00:25:09 - 00:25:33)
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: 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: It was quite obvious that the beaver was fake, and not a very good one relative to the capabilities of contemporary CGI. (The first time, the beaver was presented as real; the second time, it was meant to be comical). (00:59:20 - 01:29:13)
Revealing mistake: The ostrich had its head down, pecking on the floor, when Rachel opened the door. Rachel screamed, then the ostrich raised its head. Ostriches generally have acute hearing that enable them to hear approaching predators, so it is unlikely the ostrich (even a pet) would not have raised its head when Rachel was still on the other side of the door. Also, the ostrich showed no reaction to being so close to the foot+ high flames in the indoor fire pit, suggesting one or both was/were fake. (00:54:47 - 00:55:16)
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: During the battle of the Chosin Reservoir, just before VF-32 comes in to provide air support, the Marines are firing their M1 Rifles. One of them mimics the recoil of it but we don't see the bolt move back when he fires his rifle. The M1 Rifle or Garand is semiautomatic, and the bolt moves back each time the shooter pulls the trigger.
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 "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: Diana's dog breaks free from her captivity with the slightest push against an unlocked pen. (01:15:35)
Revealing mistake: At the hangar junkyard, there were a few 5-gallon gas containers around several "flammable" barrels that The Thief shot at in order to ignite/cause an explosion near Temple's goons. The huge explosion engulfed the whole area, but seconds later it could be seen that the flames were confined behind or within the circle of barrels and the gas cans were not affected. (01:13:10)
Revealing mistake: The very first shot of the movie, supposedly of Anya Taylor-Joy lighting a cigarette, does not match the following shot on the pier; the cigarette appears to be black and with a brand sleeve instead of the normal one she is smoking. The background confusingly looks more like an interior than the pier she is standing on, and the lighter is a common Bic-style one instead of the Zippo she is using also later in the movie. That's because it's actually stock footage. You can literally find the clip yourself on Shutterstock and similar websites, by the description "Close-up of the silhouette of a woman's face sticking a cigarette into her lips, igniting her with a lighter, and exhaling smoke. The grim concept of the harm of smoking in a low key." (00:01:00)