While most spinal injuries are caused by traumas that bruise or tear the nerves, a transplant surgeon could sever the cord cleanly with a scalpel blade. But weighed against this small advantage is the staggering complexity of joining two separate neural circuits that have neither developed nor functioned together before.

Even if the spinal cord could be reconnected, would the patient ever learn to control the new body? The brain has a remarkable capacity for rewiring itself, especially as we develop during childhood. But the “plasticity” of the adult brain has limitations.

Many amputees experience vivid and often agonizingly painful “phantom” sensations from where a lost limb used to be, even years after amputation. This suggests that our mental representation of ourselves—our body schema—may not easily adjust to changes in our own bodies, let alone get used to someone else’s entirely.

Perhaps transplant tests with monkeys may in future provide convincing support for applying this surgery in patients, although such experiments would certainly not be allowed by the strict regulations that govern animal research in the U.K. Nor should they be at present, given the severity of the procedure and slim chance of success.