Are premium-priced fuels really worth the extra cost? Why are males born with nipples? Is a male contraceptive pill in the offing? Do all animals get the same number of heartbeats? Does any one organ failing cause death? Can aeroplanes run on diesel? Why does silver tarnish? What causes lightning? Is mental illness curable? Join Dr Chris for the answers to this week's crop of queries from South Africa. Like this podcast? Please help us by supporting the Naked Scientists