Watch the film carefully. Kennedy's head was already moving in a forward direction (as though he were slumping over from the first shot from behind) when the second bullet hits him in the forehead.
A split second after that happens, his head jerks back violently, which is exactly what you'd expect a human head to do when being penetrated by a high powered round from the front.
Thank you for your reply. To me, Kennedy’s head appears to be still at the moment of the head shot (see the small motion picture on the right in the link below).
Then the stop motion of two frames shows that his head snaps sharply forward in about 1/18 of a second when hit - that is the time from frame 312 to 313 (the Zapruder film is about 18 frames per second according to a source).
http://users.skynet.be/mar/Eng/Headshot/back&left-eng.htm#Sommet
Very true, on TV. But not according to world experts in forensics and human physiological/neurological response to a gunshot. There are volumes about this subject. “What you’d expect” is verbage from movie watching supposition, without benefit of study or knowledge.
Of useful note is the time oswald had to set up the shot, the rising elevation of the vehicle (prez. head) and falling away in distance-— combined to provide a virtually “steady” position of the target for a sufficient period of time. A tragedy.