Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

More proof that it's not her left arm- at least not in that situation. I have put a line in pointing to her left shoulder- as much as we can see of it. 

Well, you know that the shoulder consists of the junction of the head of the arm bone (or humerus) and the top of the shoulder blade (or scapula). So, if that's where her shoulder is (and that is the case) then her arm has got to be attached to it. There has to be continuity and no breaks between her shoulder-her arm- her forearm- and her hand. So, where is her upper arm? 

But, there is no connection between her forearm and her left shoulder. They are separated by empty space. Where is her upper arm? 

If that's her left forearm, where is her left upper arm, and why don't we see it uniting her forearm with her shoulder? In actuality, her left arm is down and not raised at all, and that's why we don't see it. There is no connection between the jutting forearm and her left shoulder. Something is missing: her left upper arm, which must have been down.