This is where you discover some one with their chin up and you proceed with a karate chop to the neck while shout "open neck!" The person doesn't have to be with their chin up, they just need chin high enough to fit a flat hand in. You cannot "open neck" some one if they know you are going to do it or if they have their chin down a considerable amount. The whole idea about the "open neck" is supposed to be a suprise with a choke. Be careful if you decide to play this game, because it can keep going on for years to come.
"Hey, look at Shaun sitting there staring at the computer." *Nick creeps slowly behind Shaun, then moves to the side of him...*
Shaun: "Uuuugh, you smashed my throat"