The main difference between rib flaring and pigeon chest is that the former is caused by soft tissue pathology around the thoracic cage, while the latter is due to a bony deformity of the thoracic cage. Patients with rib flaring often have very thin muscles around the thoracic cage due to poor posture, such as excessive abdominal tucking or long-term dieting, which leads to a very prominent thoracic cage when standing. Pigeon chest, on the other hand, is due to severe malnutrition during the patient's growth and development phase, which leads to the anteroposterior diameter of the thoracic cage being larger relative to the mediolateral diameter. In this case, the patient will exhibit a noticeably protruding thoracic cage, especially at the front.