They look at how the muscles are contracting and pulling the spine and neck and straighten it out,
BTW, Mu Chiro told me a story, his BIL had a funny gait and pain, did not ask the Chiro for advice.
Friend says I can fix that, on the tailgate of a truck!!! His BIL is now a believer!!!!
Mine is a pretyt big guy, not fat, about 6'4" and in great shape, DO NOT try to resist, relax and let them work their majic!