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.