A small, finger-shaped tube attached to the caecum at the start of the large intestine, long dismissed as a useless evolutionary leftover. That view has softened: research suggests it serves as a safe house for beneficial gut bacteria, sheltering a reserve population that can repopulate the intestine after diarrheal illness wipes it out, and it contributes to immune function through its lymphoid tissue. Its clinical fame comes from appendicitis, the dangerous inflammation that occurs when the tube becomes blocked and infected, once a frequent killer and now routinely cured by surgical removal. Life after appendectomy is entirely normal, which kept the useless-organ myth alive. Nutrition intersects only at the margins, in the brief dietary progression back to normal eating after surgery.