The Connallys, Greer and Kellermann all testified that they were hit by blood, brain and other material that ejected from JFK's head. Connally said a piece of brain the size of his thumbnail landed on him. The front of the limo, the interior, the hood, were all covered with this blood/matter. The Zapruder film shows this blood/brain/matter exploding up and forward. As DPD motorcycle officer Bobby Hargis, riding right behind JFK, said: "If he'd got hit in the rear, I'd of been able to see it. All I saw was just a splash come out on the other side." That is, he saw no "splash" come out of the back of the head.
We have eyewitness accounts, physical evidence, x-rays, photos and a film corroborating this.
There is no way a bullet can exit/explode out of JFK's head in the back and for this to happen. And yes, I am aware of the 40 back of the head witnesses. Their accounts are not corroborated by anything else.
Or you can believe, as Dr. Mantik does, that all of this was fake, the Connallys et al lied, the films/x-rays/phots were all faked, and the examination of the limo was staged.
If you believe Dr. Mantik's claims then there is nothing to persuade you otherwise. You'll just dismiss it as fake.