Continuity mistake: When Brittany Murphy writes down the number on the glass she writes it backwards because that's how she sees it in her mind. Watch closely, though, and you'll see a perfectly normal 2 which isn't written as a mirror image of 5. Later, when Michael Douglas realizes this catch, he looks at the piece of glass again, this time from the other side, and the 2 has turned into a 5, which apparently was written in a different style.
Continuity mistake: When Michael Douglas' wife stabs the kidnapper in the chest during their fight in the apartment, she stabs him with the knitting needle in his right lung. The next shot shows them lying on the floor with the needle stabbed directly into his heart on the left side of his chest.