Aragorn's TT fall..

I've now seen The Two Towers nine times. The first time I saw it I was utterly let down. This book was my favorite and will always have a special place in my heart. Upon several viewings of it, I've come to love it as a film, but not an accurate representation of the book. I still can't help but question certain scenes from the movie though. The one that sticks out the most is the one in which Aragorn is taken over a cliff by a warg. If Jackson wants to add a scene, by all means do what you wish, but atleast have a reason for it. To me Aragorn's fall and arrival at Helm's Deep serves no purpose, not even from a cinematic view point. The only purse it covered was to let Theoden know that Isengard was on it's way....but didn't he know that? Or couldn't a scout just have easily told him?