Revealing mistake: In the last scene where Edward and Bella are sitting in the sunny field, Edward is not sparkling. (01:52:55)
Revealing mistake: After killing Victoria, Edward rips off a piece of Bella's shirt to tie around her bleeding arm. If you look at where he rips her shirt, the seam is visible where the fabric has already been cut and loosely reattached; there is a long horizontal wrinkle where it doesn't hang right from the rest of the shirt.
Revealing mistake: When Jacob is injured by the newborn vampire in the final battle, the Cullens and the Quileutes are crouched around him. The top of Jacob's flesh-colored body suit is quite visible at his waist; he is supposed to be nude after phasing back into human form.
Answer: It's a common expression. It means 'to take over'. So Seth will take over in protecting Bella in the morning for him.