Why Do We Sleepwalk?

What's more accurate, vehicle speed according to a GPS unit, or the speedometer? Also, what causes the Earth's magnetic field to flip, why do people sleepwalk and can the shrunken state of an accidentally boil-washed jersey be reversed? Join Dr Chris as he pits his wits against this week's science question selection and also discusses news of the discovery of sugar transporters in plants and a way to age a person using just a drop of blood... Like this podcast? Please help us by supporting the Naked Scientists