What colour is a mirror?

Why some people can't say their Rs; why is perception of time so context dependent; what's the nutritional value of long life milk; what determines how tall we are; why do some mirrors make you look a strange shape; why to take care with magnesium supplements to avoid explosive diarrhoea; how can fish swap between fresh and salt water environments; and why doesn't the stomach digest itself? Dr Chris Smith and Clarence Ford have the answers... Like this podcast? Please help us by supporting the Naked Scientists (thenakedscientists.com/donate)