Allegedly, the Tipu Sultan of Mysore had executioners known as Jettis, who were trained strong-men, and could kill people by twisting their heads off.
However, my source for this is a historical fiction novel, so it may not be 100% accurate. 
Christopher Reeve’s injury after being thrown from his horse shows how it can be done:
That’s not at all what the OP asked.
[QUOTE=drachillix]
You have to sever the spinal cord at I believe the second cervical vertebra or higher to decisively disrupt respiratory function if so yes, no lung control = no breathing or screaming. You have to hit high and if something else gives first, you will not be able to “rebreak” higher.
[/QUOTE]
I’m not offering myself up for experimentation, but I have an artificial spinal disk at C5-C6 that is more “loose” rotationally than the rest of my neck, so just maybe, if someone tried to snap my head off, all of their effort would be for naught.
By loose, I’m referring to how the artificial disk implant can spin 360 degrees, and its rotational and flexion range is limited by the anatomy it’s installed in, rather than any inherent mechanical stops in the device.
*Sharpe 's Tiger ? *. Cornwell’s research is usually reliable . Though I seem to remember they would also hammer nails with their fists into the skulls.
SirGalahad, that article does not describe how he broke the girl’s neck explicitly, but mentions he was strangling her with a belt. That can allow extra leverage over use of hands.
Putting one hand on chin, the other on the top of the head, and giving a quick snap motion as Hollywood depicts? Not bloody likely. Using your entire upper body (such as with the guillotine hold or a sleeper hold) and it is possible, but not nearly as easy to pull off as the Hollywood depiction. Even for a superstrong vampire/alien/whatever.
I appreciate your skepticism … there’s a big difference between skepticism and being derisive, condescending and dismissive. Some times when you meet a stranger, they’ll come off that way.
But on a serious note, I’ve grown, over the years, to not be too quick to underestimate the amazing feats of strength exhibited by humans under certain circumstances. I have a friend who worked in the oil rigs in Alaska in the 70s. He’s about my size, 5’10", 180lbs. He could, as recently as a few years ago (we’re both in our 50s), load a full 55 gallon drum of oil in the back of a pickup by himself, just him and a pair of gloves. I’ve seen him do it. That’s right around 500 lbs. It’s timing, practice, reflexes, and being really strong for your size. I guess he started with partially filled drums.
I’ve never seen a neck broken by twisting, and I doubt it’s common technique in the covert ops and assassination biz, but I’m absolutely not convinced it’s impossible. I don’t foresee many Youtube vids proving it, though.
Unbelievably scary… The incident I described happened in Ixtapa-Zijuatanejo, Mexico on the Pacific coast. I was basically standing in the surf in water about waist deep, with the waves breaking just about ‘head high’. I was facing the shore and kind of jumping up and back into the breaking waves. I had failed to realize just how much force a breaking wave (even a small one) actually has. (I’m from Houston, Tx and the surf in Galveston isn’t comparable.)
The wave literally picked me up, turned me head down and slammed me into the bottom. When I hit, my whole body went limp, from my neck down. The only thing I could do was turn my head from side to side. Fortunately, the impact didn’t knock the ‘wind’ out of me and I gradually (it seemed like forever) floated to the surface with just my face sticking out of the water.
As I gasped for a breath of fresh air, I could feel the next wave building up. The only thing I could do was take a big breath and hope that I could hold it long enough to float back to the surface. Three more waves rolled me to the bottom, each time I surfaced I would scream for help but the girl that I was with was about 25 yards from me when the first wave injured me. When I surfaced the first couple of times she was behind me and I wasn’t even able to turn myself, so that I could see her. At first she didn’t even know what had happened to me and couldn’t even locate me, since my face was all that was poking out of the water. When I sufaced for the fourth time she had got a little closer to me and I was turned around by the wave so that she could see my face.
She said that my eyes were as big as saucers. :eek:
She drug me out of the water up onto the beach, I knew enough to realize that she shouldn’t try to move me any more than absolutely neccessary and told her to leave me there and go get help.
Long story short, after about 20-30 minutes I could feel sensation returning to my extremities (up to that point, I was unable to feel anything at all) but still had no ‘motor control’. Over the next 20-30 minutes I gradually regained the ability to move my limbs. With assistance I was able to go to my room and wait for the medical assistance that had been called for. This all happened on a Monday afternoon, from that point until I returned to Houston on Wed. both of my arms from mid forearm to the tips of my fingers felt like they were literally ‘bathed in fire’. There is no other way that I can describe the pain. The Dr. from the clinic in Ixtapa came to my room and gave me an intravenous shot of morphine, it might as well have been saline. The next afternoon he came back and gave me an even larger dose of morphine and I was able to get about 4 hours of sleep. I came back to Houston the following day (Wed.) and Thursday I went to the hospital here in Houston and after some x-rays was referred to an orthopedic surgeon.
The surgeon ended up doing the cervical fusion that I described upthread.
And now you know, the ‘rest of the story’. 
Scary?.. Terrifying, is my choice of adjective. 
As noted when discussing the strength of the neck muscles, unless the body is rooted, the body will move with the motion, mitigating some of the force of the snap. This isn’t to say a person can’t be badly injured, but it is just another problem with the neck snap = death equation.
Lesson learned. :smack: Bet I don’t make that mistake again.
Since you think I’m being overly dismissive, I will elaborate on my answer.
The standard Hollywood depiction often shows about a 60 deg head turn to one side, no vertical rotation. That is done specifically to be safe, so as to preclude any injury to the actors, especially when the action will use a someone rapid twist to simulate the execution. This will not do anything, which is precisely why it is used. It is rather like depicting CPR by having the person straddle the patient and pump up and down with their elbows flexing. It kinda sorta resembles the action in question, but not really. It’s more suggestive than actually bearing any functional resemblance.
Okay, but that’s the strawman. What about any kind of head torque with your hands?
Again, coming up behind someone, grabbing their head, and trying to torque it quickly, I do not feel will be successful. You can probably injure the neck, pull muscles, but I do not think you can get enough leverage to create the clean break depicted, the instant paralysis/death.
Now for a situation that just might be possible: the victim is seated, you approach from behind so you have good stance, grab the chin and scalp, and you can apply the motion quickly, close to your body, using your upper body to torque. It might be possible, both because their body is somewhat constrained by being seated, and by your ability to apply additional torque because of being above and having the head in close to your chest.
Obviously, of you constrain their motion, you increase the likelihood. Thus chiropractors are dangerous, because their [del]victims[/del] patients are typically lying flat on a table while the head is being manipulated by the doctor’s whole upper body.
Similarly, a large man coming upon a child will be more likely to be able to do this than against another adult, both because of the leverage and the child’s smaller and weaker stature.
I was being a bit facetious with the “superstrong vampire” business. We have no idea what a superstrong vampire can do.
I wasn’t referring to you, Irishman, so, gabh mo leithscéal!
The guys I’ve known through the years who legitimately were Seals, Rangers, Special Forces, etc, were mostly outlaw bikers. The gist of their position on the topic was this: a body check, headbutt, or blow to the face distracts the victim, who is by necessity not much taller or heavier than the attacker. As I said, they mostly described lifting the victim by the head with one palm under the chin, and with a rapid motion, twisting the head, not like unscrewing a cap, but sideways in a (O) vertical orientation, trying to push the chin toward the ceiling and pull the hair toward the ground. The description includes a sort of dropping motion, like the snap of a hangman’s noose.
I’m not taking anyone’s word for the technique being effective; I suppose paralysis is more likely than a quick kill, but like I said, since some of these guys are brutally strong, I’m not taking armchair estimates of physiological forces on faith, either. The forces previously quoted in this thread to damage the neck and spine may very well relate to a tensed and ready victim, vs a distracted or surprised one. I’m still skeptical, but I absolutely consider it a possibility.
That’s the one!
I can find reference online to Jettis acting as “executioners”, but not to the specific details of their use in twisting human heads around.
Assuming it is true, it goes to show that it was considered an impressive feat of strength.
In The Long Kiss Goodnight, Geena Davis’s character over the course of the movie kills two guys AND a deer (badly hurt and suffering after she hit it with her car) by giving ‘em the ol’ Hollywood neck-twist!
Well, yeah. That’s Geena Davis. She’s like a goddess descended from the Greek pantheon. Let’s see you do that.
Stranger
Wot? 
See posts 19, 20 and 30.