During the memorial service at the high school, the speaker says that 39 students and teachers were lost. But there were 40 in the class, with four teachers, and seven people got off the plane so it would be 37 people who were lost on the plane.
When Clear was in the car that was being attacked by the electrical wires, Alex said that the car was "grounded by the tires". This is incorrect as the rubber tires are actually an insulator, hence they do not complete the circuit (ie. ground the car). Also, the car should, in theory, act as a partial Faraday cage, which means that all of the charge would be on the outside surface of the object (in this case the car), and that the person inside would be safe
At the airport, the French teacher addresses the students with "écoutez, les enfants!", which means "listen up, children". No French speaking person would ever address 16-18 years old with "enfants", "enfant" meaning a (little) child up to perhaps ten or maybe twelve years at the most.
Near the end of the movie when the girl is in the car with the electrical wires on it, the guy on the outside says "don't touch anything, you're grounded by the tires." In fact she is insulated, since the tires are rubber.
When Alex got on the plane, it was shown clearly that he had fastened his seat belt in his seat. However, when he woke up from his premonition, he could immediately get up and rush off to sit with Todd without having to unfasten the seat belt first, when Christa and Blake asked to change seats with him.
When Alex is in the safe house and begins opening the can of food, he starts opening the can with the spoon in his right hand. When the angle changes it's in his left hand, then again it's in his right hand when he goes to eat it.
When Alex throws the magazine at the owl in the window and is shredded by the fan, a piece lands on his leg. However, when the camera angle switches away and them back to his leg, the piece has changed position. It has rotated.
When the vodka is dripping through the coffee cup as Valerie Lewton walks to the computer it just drips onto the floor and leaves a trail of small drops. Later on when the computer ignites the small drops of vodka they have turned into a much wider trail. Also the coffee cup could not hold that much vodka.
Carter's car, when first we see it, is a Chevy Nova SS. You can recognize that model by the letters "SS" on the front grille. In the night shot later when Clear and Billy and Carter meet at the memorial, the "SS" is missing. Subsequent shots are of a car that matches the first car.
At the memorial service, the speaker says that four teachers were aboard the plane, but earlier on Ms. Newton explains to the police officer that she has to be let back on the plane because the students will be alone. If there really were four teachers, two teachers still would have been on the plane.
When Alex is watching the news, it shows the path of the explosion of the plane. He says "That's Tod's seat" but it was actually where he had been sitting. He then puts a piece of paper up to the TV to trace it and the path has changed to begin at Tod's seat.
When the teacher is lighting the gas under the kettle just before she dies. Reflections of three lights can be seen in the kettle. No kind of practical lighting is present in the next shot which could have created these reflections.
As Carter's car arrives at the crossing, a blank white crossbuck sign with a red border is seen. This is how the signs look in Canada (where the film was shot), but in the U.S. the signs say "Railroad Crossing".
The plane exploding is too far away from the terminal windows to shatter them. Also, the time it takes for the windows to shatter after the explosion is inconsistent with the speed of sound given the distance.
In the alternate ending on the DVD, Clear has a photo of her and Alex where one of them is holding a white rose. This is the photo taken from the beginning of the movie, but the position of the photo is not the same angle that the photo was taken from.
When Clear is looking at the picture of her and her father at the lake, the year says 1986. Beings the movie took place in 2001, and Clear is 17, she would have had to be 2 or 3 in that picture, but she is clearly around 8 in the picture.
In the scene before Terry's death, where Carter knocks Billy off his bike, you briefly see Billy in the distance riding his bike towards the camera, however if you look closely it is clearly not the actor (and presumably a stunt double).
When the 747 is supposedly in a nosedive, items can be seen falling down, toward the front of the cabin, as if the aircraft was still. The G-forces caused by a high speed dive would pull items up, toward the back of the cabin.
In Ms. Lewton's "death scene" she has one knife stuck in her chest and another that falls and rests near her waist. When Alex is taking the falling chair off of her they show three rapid shots. First the knife is there, then it's gone, then it's back again.
When the toilet is leaking in the bathroom when Tod gets strangled, the water is leaking from the water line valve not the tank. However, the water running down the tile is blue as if it came from a tank that had toilet cleanser in it. In the directors commentary, they explain that the water they used was deliberately blue so that the audience could see it better. if the water had been ordinary clear water it would be nearly invisible to the audience. However during this scene, if you look carefully you can see the floor has been built sloping down slightly obviously for getting the water to run across the floor.