The movement of Kennedy’s arms was into the ‘Thorburn Position’, a medical term for the movement of the arms along with a high extension of the elbows as a neurological reaction to trauma to the spinal cord.
It’s a fairly common symptom in combat injuries that involve temporary or permanent paralyzation of the high spinal cord region. It’s the most visible indicator to combat medics and Hospital Corpsmen that the subject is paralyzed.
Except, there was no spinal injury found in the autopsy, so there would be nothing to trigger that reflex. Yet, we do know he had a wound in the front of his neck exactly where he seems to be grasping. Grasping at such a wound, which probably interfered with his breathing, is also a perfectly natural reaction, and fits the facts better than a reaction to a non-existent spinal injury.