It's when you bend your fingers so far back that the bones snap. Pretty common in America, rather than the less painful 'clicking' made elsewhere.
I- I don’t understand. They were doing some sort of Pavlovian dom/sub kink play?
I believe that's called "puppy play."
Is this the trend now? Dog theme?
possibly pet play or hypnosis but definitely conditioning play
would recommend it's fun
either that or hypnotic suggestion