Patient “M”, from Bill Bryson’s The Body: after shingles left a four-centimeter itch on her scalp, she scratched in her sleep until one morning cerebrospinal fluid ran down her face, she had scratched through the skull to the brain. The most disconcerting part: the nerve fibers in that patch of skin are destroyed, and the itch persists. A reminder that itching lives in the brain, not the skin.