Why do veins look blue?

How much water should you drink in a day? Can miscarriages be prevented? What's more efficient - leaving the hot water on constantly, or heating it only when needed? Why are some eggs double yolkers? What's the point of flies? And why do some people have more than five fingers? Join Dr Chris for another crop of South Africa's top science questions on Talk Radio 702... Like this podcast? Please help us by supporting the Naked Scientists