Sufferers of a bizarre medical condition called “body integrity identity disorder” (BIID), who are otherwise totally sane, feel as if one of their body parts their right foot up to the mid-calf, for example shouldn’t be there. The limb seems horrific and alien, and they can usually draw a line in the exact place where they desperately wish to have it removed. The neuroscientist Vilayanur Ramachandran recently uncovered the cause of the condition: BIID sufferers are missing part of their body image map in their brains. Their unwanted limb is not correctly mapped onto the corresponding brain region, leaving them feeling extremely uncomfortable with it. There is currently no cure but for the uncharted limb to be removed, and when a sympathetic surgeon agrees to amputate, BIID sufferers report feeling infinitely happier.