Curious about stem cells? Via Biosingularity, here’s a couple of short, understandable videos:
http://www.youtube.com/watch?v=icrRFrMiEPw http://www.youtube.com/watch?v=Kq60z89rWD0 http://www.youtube.com/watch?v=VodvbRxzS4c http://www.youtube.com/watch?v=OM16PalZaj4
Sonic Hedgehog, heh.