Deliberate mistake: When Phil wakes up at 6 AM, it's already bright outside. At 6 AM in February, it would still be pitch-dark.
Deliberate mistake: In the sequence where Jack finds his friend, and then the cards he is holding counts down to the explosion. Jack runs out, and the house explodes throwing the cop car into the air. If you look close, you can see the piston that launches the cop car and then falls back down. (00:24:40)
Suggested correction: This is a scene in the "fake movie" where everything is an action movie cliche, including seeing the deliberate mistakes.
Deliberate mistake: In the scene where Sam is swinging from the hospital window, you see him first from the inside. Now he is obviously being pushed (from a crew member) so it looks like he's moving back and forth smoothly. However, when seen from the outside he couldn't be pushed and so when swinging by himself, he was actually bouncing off the walls. Inside this would have been seen. Also, inside it seems that the sky is clear, though outside there is a tree by the window.
Deliberate mistake: It's not possible for Chance to have been able to launch the cougar off the cliff with just his own weight.
Deliberate mistake: When the saloon patrons pour through the swinging doors in pursuit of Packer, the same people are seen repeatedly. A relatively small number of extras are running around to the rear of the set and re-entering through the back so that they will appear to be a larger crowd of people.
Deliberate mistake: Towards the end of the film, Josh is playing a game in the park with Vinnie, and Vinnie asks "What's that?", to which Josh replies "Schliemann Attack." However, this dialogue occurs while the game is still in standard opening theory and before Josh has played the move that introduces the Schliemann Attack (pawn to f5).