It isn't bones cracking, and it isn't a measure of how well the adjustment worked.
It's the single most asked question in the room, and the answer is less dramatic than the sound suggests.
It's gas, not bone
Joints are surrounded by fluid containing dissolved gases. A quick change in pressure inside the joint lets a bubble form, and that formation is the noise. It's the same mechanism as cracking a knuckle.
The sound isn't the goal
Plenty of effective adjustments are silent, and a loud one isn't better. What matters is whether motion improved and symptoms changed, not what it sounded like.
Is it harmful?
There's no good evidence that the sound itself causes damage, and the long-running claim that knuckle cracking causes arthritis hasn't held up. If the noise bothers you, say so, because gentler techniques that don't produce it work perfectly well.
