Originally Posted by geerussell
I saw something on this question on tv once. They did a demonstration with melons showing how they fell in the opposite direction of the shot. The reason for this was while the entry impact pushed them in the direction of the shot, the bullet creates a buildup of pressure as it passes though and makes an explosive exit leaving a huge hole and pushing the melon in the opposite direction of the shot.
Replace "melon" with "jfk's head" and you get an explanation for the head moving what appears to be the wrong way.