Ask the Naked Scientists, South Africa 13.09.27 - What Do Rockets Push Against in Space?

Summary: What colour were human ancestors? What does a rocket push against in space to propel itself forward? Why does yawning make me cry? How do bats navigate? Can fuel cells run on alcohol? Why are 90% of people right handed? How genetically related would the children of two sets of identical twins be? Plus, noses grown on foreheads and how rotating antibiotic drugs can prevent bacterial resistance...