>> As the bullet exited Kennedy’s head, a jet of pulverized brain matter followed in the forward direction and acted like a rocket, pushing his head backwards. At the same time a piece of the side of his skull blew off. The backwards movement of his head, combined with the forward motion of the car caused the skull fragment and some pieces of brain to land on the back of the car.
Discredited by many professionals both civilian and military with extensive experience in the interrelated subjects of ballistics and physiopathology.
1. Luis Alvarez, a Nobel Prize physicist, showed through experiment how what I described can occur. He also did a lot of analysis on other aspects of the assassination including the Zapruder film. Here is a description by another successful physicist of how Alvarez was by far the smartest person he knew.
2. Bugliosi pointed out that at the frame of the Zapruder film where Kennedy's head is hit, his head moves forward slightly. Therefore, since his head was hit with only one bullet, and was spraying out brain matter, the subsequent backward motion of his head, is entirely consistent with this theory.