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You are watching: How much force to snap a neck
In this particular case, I am talking about an extremely flexible human. In my story, this human catches another"s head with his legs and manages to snap his neck. I know a human can"t simply snap another"s neck (They don"t have enough strength), but could it be done if the attacker were able to pinch their opponent"s neck (to weaken it), and then twist and snap it?
It is possible in theory, but not the way it is shown in the movies. First of all, the human neck is both strong and flexible, and unless the person is taken unaware (like in a car accident), will automatically tense up in response to pressure, making it even stronger. Second, even if you could muster enough strength to break a neck, unless the rest of the body was restrained you would just end up twisting their entire body around.
The only way to pull off a snapping someones neck realistically is by getting the victim in a full-body hold, then stretching and twisting the neck until it breaks. You"d need to be very strong to do it though; flexibility alone isn"t going to be enough to snap it.
It may, however, be possible to break someone"s neck with an impact instead of a twist. A strong punch or kick may produce enough force, but only if the body was restrained somehow, so not really practical in a fight. It may be possible to get them in a hold and then throw yourself and them onto the floor with enough force to twist their neck to the breaking point, but this would involve more luck than anything. This may be the best option to use in a story though - this makes it basically a matter of luck.
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It won"t be an instant-kill in any matter; even if you fully paralyze the person from the neck down they"ll still be alive until they suffocate. More likely than not they won"t be fully paralyzed and you"ll instead be left with a paraplegic who is perfectly capable of talking (or screaming). Think about the possible results neck injuries from a car accident. Those are basically the results you"ll get from trying to do this if you dont instant kill them.(You Won"t So Please Don"t Attempt This)
All in all, this isn"t a very effective killing maneuver, even with brute force and extreme flexibility.