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

Someone suggested that Zapruder might have moved and that's why Babushka and Brehm are blurred in the one frame.

But, that is not reasonable because the limo area and its occupants are clear in both frames. If Zapruder had moved, it would have disturbed the entire frame. The motion blur would have effected everything. So, that cannot explain why Babushka is so blurry and Mary Moorman is not.