Testament of Youth (2014)

Factual error: Roland enters the train to go to the war, in 1914, with "Spanish Flu", but that was the (wrong) name given to the 1918 flu pandemic, which lasted from spring 1918 through spring or early summer 1919.

Vera Brittain: Like no-one else... you share that part of my mind that associates itself mostly with ideal things and places... The impression thinking about you gives me is very closely linked with that given me by a lonely hillside or a sunny afternoon... or books that have meant more to me than I can explain... This is grand, but still it isn't enough for this world... The earthly and obvious part of me longs to see and touch you and realise you as tangible.

Question: In the opening scene, when Vera was looking intently at a painting depiction of an underwater scene, we cut to her being underwater, taking off a coat, and then lingering underwater, looking up. What was going on that made her go underwater, take off her coat, and float in the water?