Paul Stevens made a very good observation in response to my previous post, which I also posted on Facebook.
Paul pointed out that Jackie's initial reaction was not like anything as catastrophic as a fat bullet coursing all the way through JFK's neck from back to front had happened. It was more like he got something caught in his throat. Watch the Zapruder film again with that in mind; just focus on Jackie's reaction. What I notice is that, prior to the fatal head shot, she spends much of the time with her eyes glued on Connally, like she was more concerned about him.