Why isn't Roger Federer's right arm twice the size of his left?

踢啊ff with a look at why coffee might make you live longer, Dr Chris and Eusebius explain why Roger Federer's right arm isn't twice the size of his left? How aeroplane wings form vapour trails around the wing tips, why babies kick in the womb but seem to do little after they are born, and how a crocheted blanket, or a string vest, keep you warm despite being full of holes. Plus, what was the giant iceberg that broke off recently from the Antarctic ice sheet, if the Universe is expanding, why do some galaxies collide, why do aeroplanes have black boxes when they could rely of satellite tracking, how do hippos stay submerged for so long, and what is St Elmo's Fire?