Try all the play, forward, rewind and back options to see what they do.
This is not normal behavior. See if you can figure out how to make a swf that behaves the same way.
(Bonus: make the Loop option actually do something)
my guess is you keep track of the previous frame as well as the “requested” frame of the movie. when a movie normally plays, the “requested” frame is always prev+1 right? now a simple if statement can test otherwise and call the necessary functions for playing backwards, blah blah blah…