What is involved in blood doping in sports? Can beetroot make urine red? Can mosquitoes transmit HIV? How do dung beetles use the Milky Way to navigate? Do sneezes stop your heart? Can you hear a supernova? Could plants grow on Mars? Why do ants keep drowning in my drink? Why do we not notice Earth turning? And can flour relieve burns? Dr Chris takes on another batch of top science questions from South Africa.