Continuity mistake: When Claire and Russel are arguing in the classroom, the book on the table in front of Claire changes position frequently between shots.
Continuity mistake: Series 4 Episode 50 "The Bomb Shelter" When Nate picks up Maya to comfort her after he argued with Barb, he drops the cloth diaper bag, never picking it up again. But when he walks into the house, it's over his shoulder again.
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.