Why is space dark; do bags of coins deter flies; why don't cats go grey; is GPS or an odometer more accurate; what was the effect of the Med drying up in the past; what does an ice-pack versus a hot-pack do for an injury; how might maternal diabetes affect a baby's future health, and should I let the tap run before drinking any water? Plus, urine-powered electricity supplies... Like this podcast? Please help us by supporting the Naked Scientists