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First this week is another A-Z, where John gives us a quick guide to stem cells, before clueing us in on some new breakthroughs. You could become...anything?! Marty leaves another stellar voicemail, this time about tennis sensation Roger Federer and his hairy (and smelly) back. Let's hope the boys can sort that one out without it getting too gross. Finally, another Roleplay Problem, in which Michael's a little bit frightened of his Roomba. I really hope he can keep it together long enough for Barrett to help him out.