Emilie De Ravin is very short and her leading man is tall. Throughout the movie,she wears shoes with 8-inch heels and she stumbles around, looking like she has a distinct limp, while clutching objects and her co-star's arm to keep her balance.
When they arrive at the cemetery, Phoebe and Duncan are in a BMW 6 series. When the car explodes, you can definitely see that it's not the same car, it's actually a much older type of BMW, and also perhaps a lot cheaper one.
When the mom goes into the kid's room at the beginning of the movie, there is a stuffed lamb that disappears when the shot changes and then reappears in the next scene.