Two little things on this
First, if you want to discuss the Zapruder film, you must get the copy released as "Image of An Assassination"--- this is the ONLY copy on Earth made by going back to the original print, and taking photos of each frame as 5cmX5cm high-resolution slides. There are four versions on the DVD-- one of which shows the "never seen" area in between the sprocket holes on the left-hand side, and two of which were assembled using Kennedy's head as the centering point, instead of the frame edges (removes camera and shutter shake).
If you haven't seen this material, then you might as well discuss a drawing of the film made by someone who saw it once, somewhere--- the difference is nothing short of earth-shattering. THEN you can make your analysis and conclusions.
As just one little example of this; recall how Kennedy raises both hands towards his throat after the first hit? Well, from the versions I had always seen before ("high-quality" or no), it looked like he was actually touching his throat--- and I could never tell for sure either way. Well, watching this version there is absolutely NO question--- his hands are both at least six inches from his throat. That's just one example of what this kind of clarity does for your examination--- based on that one observation I later found out that it is characteristic of bullet injuries high on the back--- those muscle movements are, for the most part, involuntary reactions to the muscle trauma.
Just one other little point that stood out to me, and shows the difference between this and other versions of the film you may have seen--- BOTH the victims are completely free of the Stebbins Freeway sign when the shot that hits both of them comes along--- most people think it happened when they're still behind the sign. It most emphatically did not; and seeing it clearly will also permantently set your mind at ease about the question of whether or not it was a single bullet--- it was; and you can see them both react to it in the same instant of time... it's like a bee suddenly zipped through the car, they both jerk convulsively at the impact.
I will leave you to make your own observations and conclusions, but please--- do get ahold of the best source material. You're just spinning conjectures with anything less. Especially these fine points about scissoring legs and whatnot... you simply will not be able to tell for sure what you're seeing otherwise.
The issue of provenance or "doctoring" of the film I will not address here; suffice it to say that ANY analysis made off of a YouTube video (compression artifacts, anyone?) is back in "my kid saw it once and made me a very accurate drawing with crayons" land.
The provenance of the video I'm discussing here is discussed, at length, on the DVD--- make of it what you will.
The other point I'd like to make, seperately, has to do with the existence (or non-existence) of a "grassy knoll shooter," but perhaps now is not the time. I know this is one of 'those issues' that people get very passionate about, and my goal here is merely to elevate the debate by encouraging the use of the best possible source material. I believe, though, that I've discovered a very compelling reason why, second shooter or no, there is virtually no possibility any firearm was discharged from the 'fence' area on the grassy knoll.
If anyone's interested in hearing about that, just ask...