Revealing mistake: When Bella agrees to drink human blood to save herself and her baby, she says: "I'll try anything." If you look closely at her mouth when she speaks, you can see that even prior to her first sip of blood, there is a red substance between her teeth from a previous take.
Continuity mistake: Charlie hands Bella off to Edward at the altar, she is carrying her bouquet, the next shot is from behind them, Bella, Edward, and the pastor in the shot, she still has her flowers. In the next frame, from the front, it's Bella, Edward and the pastor's back, flowers are gone, and they never show up again. She didn't hand them off, there was no one to hand them too.
Other mistake: Emmett states that the Cullens "haven't hunted in weeks", meaning all of the vampires should have black eyes. However, all of the actors still have their golden contacts in. This is especially noticeable on the Blu-Ray.
Continuity mistake: During the honeymoon, Bella jumps on Edward's back to jump off the waterfall. At the top of the waterfall she is wearing tennis shoes. When she lands in the water she is barefoot.
Continuity mistake: When Alice is putting in Bella's hair clip before the wedding, she puts it in once, and the shot changes angle and you see her put it in again. It's because the girls change places too, first Alice is on the left and Rosalie is putting the clip in her hair, it pans out and back at them and then they are on opposite sides and Alice is putting the clip in.
Continuity mistake: When Jacob runs outside the Cullen's house to stop the wolves from fighting them. He leaps off the steps and runs towards them. Before the shot changes he is right beside Edward and another wolf, however, in the close up shot of him saying "Stop!" suddenly he's in front of Edward.
Continuity mistake: As Edward and Jacob are working to revive Bella just after she gives birth, Bella's eyes keep changing from being open and unblinking to tightly closed. The "making of" documentary on the "DVD Extra", showed a life-size dummy of an emaciated Bella with closed eyes that was used in more physical scenes. You can tell it's the dummy whenever Bella is shown with her eyes shut.
Continuity mistake: After Renesmee's birth, there are two smudges of blood on Edward's right cheek. While Edward works to transform Bella, the blood spots appear and disappear between shots.
Continuity mistake: When Edward transforms Bella, he bites her neck first, then her arms, and so on. In the very next close up of Bella, there are no bite marks in her neck at all.
Continuity mistake: Right when Bella's transformation begins her hair is bushed above her shoulders then next shot her hair is under her shoulder, then when her hair is changing color it's back on her shoulder.