Continuity mistake: After Rudy asks Brian and Nick where everyone went, it cuts to everyone in the cabin. In the establishing shot, Dinah can be seen in the seat in front of Albert and is sitting on the armrest. The camera then cuts to a closer shot of Albert, and the seat in front of him is visible in the corner of the shot, but Dinah cannot be seen in it. (00:27:37)
Continuity mistake: When Nick grabs onto Toomey's nose with his fingers, his thumb can be seen pressed against one of the fingers he is holding onto the nose with. When Gaffney walks over to them so that he can take Toomey back to his seat, his thumb is away from the other fingers. Then a few shots after that, his thumb is pressed against the other fingers again. (00:16:22)
Deliberate mistake: The surviving passengers are all awoken from a deep sleep after Dinah realises the other passengers have gone. Yet none of them appear drowsy or tired and none of their eyes appear strained, despite having just woken up so suddenly. (00:09:20)
Continuity mistake: Dinah starts pressing a button after realising her aunt has disappeared. She is pressing the button with her right hand and has the left hand at her side. But in the shot where she goes to stand up, she suddenly has her left hand placed under her right hand. (00:08:28)
Continuity mistake: When boarding the plane, the airport manager puts Brian's bag into an overhead bin. Standing next to him, Rudy can be seen opening an overhead bin and his hands are placed on the door whilst he opens it. In the next shot, his hands are suddenly inside the overhead bin, putting his bag inside it. (00:06:25)
Continuity mistake: When Nick bumps into Laurel, she drops her bag. When she goes to pick it back up, her hands are near the lower half of her body. When the shot cuts to Nick, her hands are now raised to be level with her chest. (00:03:15)
Continuity mistake: When Nick tells his associate he carries out the hit, the associate grabs onto his shoulder and is shown pulling on the collar of Nick's shirt when he does so. When the camera changes angles to focus on the associate, Nick's collar doesn't appear to be getting pulled on at all. (00:01:43)
Continuity mistake: When Brian is about to fly back through the time rift, there is a mixture of blue and orange lighting coming from the rift that is cast on him and the wall behind him. When Nick rushes into the cockpit to tell him to turn back, in the close-up of Brian, the wall behind has blue light on it. When the shot cuts to have Nick and Brian in the frame, the wall now has orange light on it. (02:33:43)
Answer: In the book he slaps her across the face during a heated argument. I can only assume that is what he is talking about.