Often patients will hear a "pop" during a traditional chiropractic adjustment, and sometimes during a Cox Technic flexion-distraction adjustment. This "pop" is called a cavitation. This cavitation is simply a release of gases (oxygen, nitrogen, CO2) from the facet joints of the vertebral segments which contain synovial fluid. Synovial fluid lubricates the spinal segments for movement. Consider opening a soda bottle that is dropped. When opened, there is a loud snap and rush of bubbles. The cavitation is similar, but contained.