(at around 16 mins) When Linda Stiles is introduced for the first time and is speaking about Sutter Cain's book, she takes her glasses off and folds them twice.
At the church, Simon fires his double-barrel shotgun three times without reloading.
It is highly unlikely that Trent could draw on his padded cell wall's with all the crosses with a single crayon and no ladder.
(at around 14 mins) When the axe-wielding madman is shot several times by police men, no visible bullet marks are made by the gunfire.
(at around 1h 11 mins) When Sutter Cane peels himself away to reveal the abyss, although most of his upper half is no longer "in reality" his shadow on the wall behind him remains perfectly intact.
The bar code for the book being printed out in the open ending sequence is "1234567890"