When Jimmy and Mary are talking in their kitchen he is facing the camera and passes her the can opener. The camera shows a closeup of Jimmy and he doesn't appear to move but when the view changes back to the two of them, he has turned to face Mary.
When Sam is researching the building on the Internet, the article she reads spells architect wrongly.
In the opening scene, when Julie is being buried, her left hand is covered in cement. On a close up of her banging the wall, her left hand is clean.