Some hand washes claim to kill 99.99% of all germs. What do these advertising slogans really mean? Would two hand washes kill 100 per cent of all germs? Plus, we ask if sending an e-card is really more environmentally friendly than a paper one. Like this podcast? Please help us by <a href="https://www.thenakedscientists.com/donate">supporting the Naked Scientists</a>

Is an e-card more environmentally-friendly?

Each week we set out to solve one of the world's weirdest, wackiest, funniest and funkiest scientific puzzles. And along with the answer there's a brand new question to think about for next time...