At the airport, Nicholas gets ink on his shirt. When trying to clean it, it's a different shirt.
Christine spills wine on herself and Nicholas, but it soon disappears from her shirt.
A man appears out of nowhere outside of Nicholas's house, giving him a good scare. In a second shot it is revealed to be Sean Penn's Conrad character, but in the first shot a different actor is used.
When Nicolas is watching the film strip, he gets fed up and stands. He looks back and clearly is standing in the way of the film's projection onto the screen, but when the screen is shown there is no shadow.
When the detective follows Nicholas from the hotel, there are sometimes two people in the car.
Nicholas van Orton's assistant tells him the number of the Nikko hotel, which is 555 1111. When he dials the number on his cellphone however, the DTMF tones heard are for 465 2222.
In the end credits, there's an extra space between actor André Brazeau's first and last names.
When Nicholas Van Orten is on the phone with his bank he gives his password as: "Blue, 2, backslash, 9690, D as in David." This would be written as: Blue 2\9690D. However, the chapter title for this scene uses a forward slash: Blue 2/9690D.
When Nicholas gets off the truck in San Francisco, it's daytime. When he arrives at his house, it's nighttime. However, seeing as how he walked the distance from the middle of the city to his house, it would have taken him several hours to arrive at his house.
Nicholas Van Orten's birthday is in October, but in one of the scenes as the car goes by a Hallmark Store it clearly is advertising "FATHER'S DAY" (which is in June).
During the in-car shots in the sequence where Nicolas is being followed by the P.I., the speedometer of the BMW stays at zero.
When Van Orton and 'Christine' leave from his office in separate taxis, Christine's cab stops just off-camera - the reflection of the brake lights from the cab can clearly be seen in the bumper of the remaining taxi.
In the last scenes, when Nicolas breaks glassed roof, one of the thinner beams hits support beam. The support beam wobbles like it was made of elastic material.
Nicholas' lips don't move when he apologizes to Christine after everyone runs away at the fake hospital.
Christine's lips are not moving when she delivers one of her lines as she discusses the possible consequences of the "Game" with Nicholas in the car.
When Nicholas goes to Christine's apartment in Potrero Hill, he discovers that it's fake when the water won't turn on. It makes little sense that CRS would spend hours inside that apartment staging it and not have any running water, but CRS actually wanted Nicholas to discover that the apartment was fake - several other clues had been left for him. Nicholas' discovery starts the chain of events that lead to the shootings and the car chase - all things that CRS had planned for.
Michael Douglas would have died or have been critically injured from the fall from the building.
When the "news anchor" is speaking to Nicholas through the TV, Nicholas begins to pry apart the TV in order to find the camera, and the man on the TV looks directly to his lower-left, right at where the panel is being broken off. This would only make sense if the camera were mounted on the TV; however, it is shortly revealed that the camera is located across the room from where Nicholas and the TV are located, not mounted on the TV itself.
The sign on the gate to Nicholas Van Orton's house says for auction due to "forclosure" - should be spelled "foreclosure".
While speaking to his ex-wife on the telephone, Michael Douglas makes the mistake of pronouncing the word "nuclear" as the incorrect "noo-kyoo-ler". (A mistake he also makes in The China Syndrome (1979).)
When Conrad (Sean Penn) finds the CRS keys in Nicholas's car he shouldn't have acted as surprised as he did, considering he was in on The Game too.