Revealing mistake: During the subway scene, when the first pillar breaks and starts to move towards Dorothy, the top of it is cardboard and wiggles back and forth as the pillar breaks. This is noticeable in the other pillars as well.
Revealing mistake: While Billy and Eli are on the river, with Eli in the front and Billy in the background, pay attention to Eli's paddle. When it passes in front of Billy, you can see right through it to see Billy through the paddle. (00:56:25)
Revealing mistake: When Jake reactivates the old biplane at Daley's Airport and Wilson mounts it as it takes off to pursue Olympus, you can see the wires from which the skeletal plane is hanging. (01:29:20)
Revealing mistake: When Tony is stacking the wine barrels in Gannon's lab, you can see the wires pulling the last barrel up into the pyramid.