Dan, yes that’s it, good eye. I saw it on some MPI frames but it is on this gif as well.
The cuff disappears down the same time the orientation of his hat starts changing around, presumably following the wrist/hand motion.
To me it looks like the wrist was driven down after aperture closure of z222 and before it opened for frame z223.
I agree his wrist orientation a few frames later looks weird. I had heard he held the hat all the way to Parkland. Perhaps wrist strength/flexure and finger grasping strength/flexure are different enough to allow a finger grasp to exist after wrist damage.
This is correct. In the book “The JFK Myths” Larry Sturdivan explains that the bullet shattered only one of the two forearm bones, the radius, but not the other bone, the ulna. One nerve was cut, but it was a sensory nerve, not a motor control nerve, so he was still capable of holding the hat, and is seen still holding his hat just after the head shot at z312 when a few frames later the wrist and the hat drop below view. But his wife said he held onto the hat all the way to the hospital.
So, I would suspect he would not have been able to hold up a bowling ball but keeping a grip on the hat was no problem.