A question we are asked a lot!
When spinal joints are manipulated they produce a characteristic pop or click sound. Neck joints, especially, sound loud because they are quite close to the ears!
To start with, the pop sound is NOT the sound of bones breaking. Actually, the joint itself (which is where two bones meet) produces the sound when the stretching of the joint reduces pressure enough for dissolved gases in the joint fluid to bubble out and produce the pop.
It's a bit like opening the top of a coke bottle (reducing the pressure) and seeing the bubbles form.
So the pop sound is a naturally occurring sound made when a joint is stretched.
Any so-called 'synovial' joint can make a pop - the art is in making stiff restricted joints move better through precise manipulation.