Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on individuals as a preventative surgery for such problems. A special case is that of congenital amputation, a congenital disorder, where fetal limbs have been cut off by constrictive bands. In some countries, amputation of the hands, feet or other body parts is or was used as a form of punishment for people who committed crimes. Amputation has also been used as a tactic in war and acts of terrorism; it may also occur as a war injury. In some cultures and religions, minor amputations or mutilations are considered a ritual accomplishment. Unlike some non-mammalian animals (such as lizards that shed their tails, salamanders that can regrow many missing body parts, and hydras, flatworms, and starfish that can regrow entire bodies from small fragments), once removed, human extremities do not grow back, unlike portions of some organs, such as the liver. A transplant or a prosthesis are the only options for recovering the loss.