Revealing mistake: At first glance, the cow at the start may have looked real, but its limited mouth movement while eating grass (without any grass being pulled out) indicates it was a mechanical cow. The cow also did not move its rear end or raise its head when Fenn and Geary approached and stood right behind it. A real cow would not stay in the exact same position (motionless) that amount of time. The cow's "fur" also did not look real. (00:02:50 - 00:03:24)
Revealing mistake: DEA Agent Rick Bowden was already seated "in the best position" before knowing where Ross would sit in the SF library. Chris Tarbell already had a surveillance camera behind the seat Ross chose, giving him a clear view of Ross, also before knowing where Ross was going to sit. Even if there were cameras in other positions, the DEA Agent and Chris Tarbell being at the right spots in advance was too coincidental to be by chance alone. (00:02:09 - 00:02:30)
Revealing mistake: When the McDonald's bag could be seen setting on the desk, it was about as high as Slahi's chest. When there was an angled view of Slahi from the chest up, the McDonald's bag was as high as his neck (and, obviously, not setting directly on the table). (00:20:20 - 00:21:23)
Revealing mistake: During the attack on Druig's village, there's a shot of Gilgamesh and Thena running towards the camera, then stopping as two Deviants fly over them. During this scene, you can see Don Lee (Gilgamesh) briefly look straight at the camera (he's not looking at either the village or the Deviants, since they headed in the opposite direction). (01:13:50)
Revealing mistake: Some views of Malik driving show him, as well as Jay in the back seat, on the opposite side of the car (mirror image). (00:36:55)