Continuity mistake: When Sophie is in the lady's room and Alex has her change her clothes so she can confront her ex-boyfriend in style, her hair changes dramatically from shot to shot, from being smooth and fairly neat to being frizzed out and messy, and then smoother again. At no time does she actually brush or comb it.
Continuity mistake: When Sophie and Alex are in the coffee shop, there is a shot of Alex (over his shoulder) and he has his hand around his coffee cup. In the next shot (facing Alex) he is not holding his cup, but then he picks it up. In the next shot (again, over his shoulder) he is not holding the cup. And in the next shot (facing him), he is holding it again.
Continuity mistake: In the scene where Alex is singing the duet with Cora, there are numerous occasions where the positions of Alex's hands don't match from shot to shot. For instance, in one shot he'll have both hands on the microphone, then in the next it's only one, then back again in the next.
Continuity mistake: In the scene where Sophie pricks her finger on the cactus, she puts all the plant cleaning items on the piano and Alex picks them up again. The watering can is in his right hand, but when the shot goes to Sophie and then cuts back to Alex, the watering can is tucked under his left arm and he's holding the cleaning fluid in his right hand.
Continuity mistake: When Hugh Grant is performing his song "Meaningless Kiss" for the 'Class of '87 Reunion' - during the intro to the song, a shot is taken from the side of the stage where the manager is standing. The headphones are shown resting on top of the mixing desk. It then switches to the manager who has the headphones up to his ears - which he then puts down onto the mixing desk.