Clamp down.

This may be a zoo worker's worst nightmare. Last April, Chang Po-yu was tending a crocodile at a zoo in Taiwan when the 200 kilogram (440 pound) reptile chomped off his left forearm. Chang and his detached limb were rushed to a hospital.

To reattach a severed limb, doctors must act swiftly. "The amputated part will start to die right after it is severed," says Dr. Marybeth Ezaki, director of hand surgery at Texas Scottish Rite Hospital for Children. One reason: Severed arteries lead to a loss of fresh blood supply, which ferries oxygen to cells. Without oxygen, all of the detached arm's cells could die, says Ezaki. "After about eight hours, it would be useless to try to reattach the arm."

To prepare for surgery, doctors carefully cleanse both exposed ends of the cut. That's because dirt and germs--and in Chang's case, bacteria in the saltwater crocodile's mouth--can get into the wound and cause infection. Next, the doctors trim any damaged tissues and crushed bones. The neat edges allow doctors to more easily rejoin the limb.

When it's time to reunite the severed limb with its owner, doctors quickly connect the ends of the broken bones. How? Depending on the size of the bone, "sometimes thin stainless steel pins or wires are used," says Ezaki. "Other times we use plates and screws." Then, doctors suture, or medically sew, the ends of the soft, severed parts together. Using microscopes and fine needles and thread, they reconnect the arteries and veins to restart blood circulation. Then, starting close to the bone, they work outward to reconnect muscles and tendons (tissues that connect muscles to the bone) and nerves, before sewing up the skin.

After a six-hour surgery, Chang was reconnected to his forearm. Unfortunately, scar tissue and stiffness in the muscles and joints may keep his arm and hand from moving normally. Chang fears that he won't be able to resume his hobby of playing the piano.