A knife at your throat from behind is a serious threat to your life [understatement]. If the person wants your possessions [money, jewelry, car, etc …] give it to the assailant. They can all be replaced. YOU CAN’T! However, here are some initial responses that can be used to get the knife away from your throat if you have to defend yourself. You must immediately continue on with a follow-through technique to remove yourself from imminent danger.
Four initial responses are shown below. There are others. The responses are graded from “OK” to “BEST”. In reality, however, what works best for you is dependent upon your knowledge, skill, experience and yes, strength.
Thanks to Roy Gutierrez for being my uke and Marc Kolodziejczyk for the photography.