Continuity mistake: In the extended edition of The Two Towers, during the 'Elvish Rope' scene near the beginning, the mist disappears and reappears between shots. When Frodo falls and lands at the bottom of the ravine, there is lots of thick, white mist swirling around, but when it cuts to a wider shot, it has nearly all disappeared within a second. In the next close-up shot of Frodo, it has reappeared again.
JBrock
13th Feb 2013