Inspiration: as chest expands, the detached part of the rib segment (flail segment) moves in a paradoxical manner. It is pulled inward during inspiration, reducing the amount of air that can be drawn into lungs.
Expiration: flail segment bulges outward impairing the patients ability to exhale. Mediastinum shifts back to affected side.
The constant motion of the ribs in the flail segment at the site of the fracture is incredibly painful, and, untreated, the sharp broken edges of the ribs are likely to eventually puncture the pleural sac and lung, possibly causing a pneumothorax