为什么n't tennis players get one massive arm?

Which is better, male or female? Why does one nostril sometimes seem to work better than the other? Why do some birds hop but others waddle? What's monosodium glutamate and what does it do to food? Why are other people's farts harder to tolerate? What causes multiple pregnancies? Why do we sometimes feel cold? And why don't professional sportsmen, like tennis players, not end up with one massive dominant arm? Join Dr Chris Smith and Lester Kiewit for the answers...