Movie Mode turns the mouse into a movie controller so that you can play the movie and set key frames - all with the mouse. When the mouse cursor is in the window, the left mouse button increments the movie backward a frame per click, the right mouse button increments the movie forward one frame per click, and a thumbwheel (if available on your mouse) will scroll backward an forward through the movie. When the mouse cursor is over the play bar along the bottom of the movie window, the left button jumps the movie to any clicked spot on the play bar, and the right button toggles key frames on and off.