During the Vietnam War, the directors of the museum in Hanoi decided to hide their nation's valuable art work to keep it safe from the war. But they wanted to maintain their cultural pride. So they came up with an ingenious plan: hide the originals and fill the museum with well-crafted copies or forgeries. Now, curators at the Museum of Fine Arts in Hanoi have found that their walls are still covered with fakes. Where are the originals? We turn to Lawrence Pollard, BBC arts correspondent.