When Sam is killed the scene shifts between the dead Sam with Demi Moore and Sam's ghost looking at the dead Sam. With Demi Moore his head is completely back with his eyes looking straight up. In the scene with Sam's ghost his eyes are looking up and forward.
Once again Burak, dead people twitch and sometime move a little. It has to do with nerves sending impulses to the muscles once dead. How can a chicken run with no head? He could have twitched his last twitch.