When the rain-soaked cars enter the warehouse, the floor already has wet tire tracks, evidently from a previous take. Once they stop and the people exit, the floor behind the cab and back towards the door is dry.
In the first scene, Saito spins Cobb's totem clockwise. When the same scene is shown at the end of the movie, the totem spins anticlockwise (counterclockwise).
When Arthur arrives in the hotel to get Cobb for their ride on the roof, it is dark outside. When they are out on the roof, it is around noon.
In the warehouse scene between Cobb and Ariadne, a Nikon DSLR camera on a desk behind Cobb disappears and reappears between shots.
In the warehouse, while Cobb and the team are talking about the idea of inception, Cobb rolls up his sleeve, then starts rolling up the next sleeve. The camera cuts away, then moves back to Cobb, who is rolling up his sleeves again.
When Ariadne and Cobb are at the café, a man in a yellow jacket passes behind Cobb. The camera switches back and forth between Cobb and Ariadne several times. When it switches back to Cobb, the man in the yellow jacket passes once again. The person in the jacket is a projection and based on what the movie explains, projections behave a lot like extras. This means the same projection may reappear like that.
When the bus on the bridge hits the guardrail, it flies horizontally for some time, but the passengers immediately become weightless. That is correct; weightlessness is caused by acceleration, not speed. Falling is a vertical acceleration, and gravity will immediately cause the bus to fall as soon as it is no longer supported by the bridge.
The characters dream during a 10-hour flight from Sydney to Los Angeles on a Boeing 747. In real life, a 747 flight from Sydney to LAX takes at least 13.5 hours. The characters need 10 hours to complete the inception, regardless of how long the flight takes.
On the flight from Sydney to LAX, a flight attendant gives Cobb a white I-94 immigration form, for people coming to the US on a visa. US citizens only need to fill out a smaller blue customs declaration form. Cobb clearly declines the white form. The flight attendant also offers Fischer an I-94. He takes it and sets it down. Fischer is an Australian citizen; his passport is visible when he sits down and Cobb looks at it. Australia is a member of the Visa Waiver Program, so Australians do not need a visa to visit the US. However, flight attendants regularly give immigration forms to passengers who don't need them. Plus, depending on Fischer's position in his father's company, his visit could require a B1 (visitor for business), L1 (intra-company transferee), or E1/E2 (treaty trader/investor) visa.
When the train engine hits the cars, it is clearly affected by the mass of the cars it pushes, and its bouncing movements suggest some form of suspension (or rubber wheels). A real freight engine weighs more than 100 metric tons, far more than the cars it hits. It would not give way or bounce when hitting cars. However, the train appears in a dream, so the laws of physics may not apply. Further indication of this is that the train's wheels are shown running on non-existing rails in/under the asphalt. In real life it would not continue in a straight line.
When Ariadne is asked by Cobb to draw a maze she draws 2 that are easy to get out of, but she draws a 3rd that's impossible - the only two ways out of the maze from the center are dead ends.
When Ariadne starts changing her first dream with Cobb, she steps over an invisible step (probably a part of a green screen) each time she moves a mirror.
In the falling van, Arthur is sleeping without the headphones that were placed on his head. The headphones reappear before the van hits the water.
One car explosion is shown twice. First, the car explodes in a fireball, filling the frame. Minutes later, the same car explodes in the same fireball but as part of a bigger shot from further away in the bottom half of the frame.
When the white van emerges from the warehouse, the passenger side mirror strikes the warehouse door. In the next shot of the van's exterior, the passenger side mirror is fully extended and instead the driver's side mirror is flipped back. In subsequent shots, the correct mirror is flipped back.
When Cobb confronts Mal at the hotel, in front of the open window with billowing curtains, a crew member's fingertips can be seen through the sheer fabric.
When Arthur arrives in the hotel to get Cobb for their ride on the roof, the reflection of the window reveals a moving boom pole, possibly a C-stand and the boom operator himself.
During the chase sequence in Mombasa (filmed in Morocco), the cars' steering wheels are on the left. In Kenya, where Mombasa is located, steering wheels are on the right.
Saito's helicopter takes off from a rooftop in Tokyo, with the distinctive red and white Tokyo Tower in the background of several shots. But it lands moments later at the ultra-modern Farnborough Airport in England, more than 5,900 miles away.
During the overview shot of Tokyo, a police car siren is heard in the background audio. This style of siren is used by American police cars, not Japanese cars.
After the initial dream sequence, on board the bullet train, Cobb states that he's "...getting off at Kyoto." In the next establishing shot, we can clearly see that Cobb is in Tokyo (judging by the presence of Tokyo Tower). Kyoto is over 200 miles away from Tokyo.
In Mombasa, the cars have yellow license plates in the front and back. Kenyan cars have white plates in front, and yellow plates in back.
It was very silly of Cobb to insist that Ariadne reveal her faster route to him. He should have just asked her whether she had a faster route, and when she replied in the affirmative, told her to inform Eames and Eames alone of this route's specific location. This would ensure that Mal could not show up to throw a spanner in the works.
One newspaper article about the strained relationship between Maurice and Robert Fischer misspells "success" (with only one "c") and uses the phrase "eminent death" instead of "imminent death".
Dom slipped the sedative into Fischer's drink on the plane. The flight attendant, who was in on the plot, could have slipped it in beforehand, with much less chance of detection.
Both Cobb and Eames mispronounce the name Mombasa as "moombasa". If Eames lived there he would know this.
Some characters pronounce Saito's name as "Say Toe", whereas others say "Sigh Toe".