Continuity mistake: When they escape from the building in the first dream, the right-hand mirror of the van is broken by the narrow gate. In the following shot when they are driving, the other mirror is broken and the right mirror is suddenly undamaged. (Not due to flipped shot, note license plate.)
Deliberate mistake: During the mob scene outside Saito's love nest, the same black Saab is seen getting firebombed twice. It was shot from two different angles, with the two shots played about a minute apart to give the impression of two cars getting bombed. Also, in the first angle it is clear the car has no engine.
Revealing mistake: When Ariadne is pulling the two huge mirrors close together underneath the bridge with Cobb, watch her when she is closing the second mirror. She steps over something even though there is nothing present for her to step over. There must have been a green screen frame there for her to step over.
Continuity mistake: At the beginning of the movie, when Cobb and Arthur are on the top of the building about to get into a helicopter to leave, they find Saito in their helicopter. During the dialogue between Saito and Cobb, the window of the helicopter behind Saito is wet and being rained on. But when the camera cuts to Cobb outside the helicopter, it is not raining at all. This happens multiple times in the scene. As the helicopter flies away at the end of the scene, there is no rain.
Visible crew/equipment: During the zero-gravity fight scene in the hotel room, it is possible to see a crew member's hand briefly resting against the end of the bed when Arthur and the projection are fighting on it.
Continuity mistake: As the van is in free-fall from the bridge to the water, Arthur's headphones disappear and then reappear between various shots.
Continuity mistake: Third dream level, there are six henchmen being pulled by the Hummer snowmobile, and the back right gets shot off (or taken out). A scene a few minutes later, the missing henchman is back, then a few minutes later he is gone again.
Continuity mistake: When Ariadne is learning how to make/change terrain, she shifts gravity and makes buildings touch the top of other buildings. However, if you look in the windows of the black hatchback or any other car, you can see sky and clouds visible.
Deliberate mistake: The exact same filmed footage of sleeping Arthur is shown in two different scenes inside the van. This repeated slow-motion scene shows his left hand rising and two spherical droplets of water drift towards his right eye. It can be first seen when the van is being chased out of an alley and makes a right turn onto a street. Then is can be seen again soon after the motorcycle rider smashes into the windscreen. Watch for it when the van passes through open gates and makes a right turn.
Continuity mistake: In the scene where Ariadne finds out that the only way Cobb can dream is by being hooked up to the machine. When she first walks in and sees him sleeping on the chair she has a purse over her left arm. But in the next shot, she has no purse on either shoulder and their no shot showing her putting the purse down.
Revealing mistake: In the scene and shot were Arthur explains how to create the looping architecture. On the staircase reveal - as the camera comes to a rest at the end of the "crane down" the entire stair case wobbles at the end of the shot.
Continuity mistake: As Cobb is finishing describing how powerful a dream is, his right arm hangs down out of sight as his left thumb touches his forehead, then drops to rest on the table. A wine glass stands to his left. When the viewing angle reverses, his left arm is instantly hanging so that the hand is in his lap, and his right hand is bringing the wine glass to his mouth, yet the conversation is real-time continuous.