This week we're exploring why swimming on a full stomach might cause a cramp, whether it's really true that joints ache more when the weather's cold, and why does tapping the top of a beer bottle make the drink explode? Plus, why do aeroplanes fly high if there's less oxygen for the engines and less air for lift? And why does a child's hair often darken as they age? Join Dr Chris and Kieno Kammies for this week's Ask the Naked Scientist, to find out! Like this podcast? Please help us by supporting the Naked Scientists