I was talking about the head going through the other day with my friends. I personally found the head reuniting with the body and turning into a 'Ghost Rider' terminator the worst part, not the actual time travel. Two of them thought it was stupid because why wouldn't other metallic objects like the gun go as well. I argued that a skin and blood covering on the head wouldn't make a difference on a terminator and the machine MUST be configured to take humans and terminators, otherwise Cameron would not go through.