Where Grey matters!
According to the book, Frodo and Sam were never at Osgiliath. So Peter Jackson admits that he took a bit of cinematic liberty and modified this part from the book
When Frodo and Sam are in Osgiliath, Sam says, "By rights, we shouldn't even be here." This was a nod to the deviation the screenplay had taken from the book's storyline. In the book, Sam and Frodo never passed through Osgiliath at all. < Copied from IMDB - LOTR 2 Trivia :D >