Continuity mistake: When Nate is comforting his mother in the side room, a bracelet on his right wrist disappears and reappears multiple times.
Continuity mistake: Right at the end when Nate is looking at people passing by on the street, his facial hair is thicker in some shots than in others. This is because they had some reshoots, as explained by Alan Ball in the commentary.
Visible crew/equipment: As David walks to open the main door of the funeral home, there is masking tape to mark where the actor is meant to step.
Answer: Nate actually say "You can't take a picture of this, it's already gone." It's kinda hard to explain, but he's referring to the fact that the moment Claire wants to take a picture of is over already, and she can't take a photo of it, just a different, lesser moment.