In the library sequence, the books on shelves are moved during conversation.
In this movie, set in Arizona, all the cars shown have front and back license plates. However, in Arizona you are only issued two license plates if you have a personalized plate which none of the cars in the movie had.
When Leland is watching the basketball game with the other inmate, the sun is shining through the window, however, the shadows outside are cast in wrong direction.
In the scene where Becky and Leland are walking at around 2 in the morning, in the background you can see it begin to rain, but both Leland's and Becky's clothes remain perfectly dry.
It is not explained how Allen obtained the knife.