5. Why Doesn't The Doctor Just Always Cut Off His Hand?
When the Tenth Doctor was reunited with Rose Tyler in the Series 4 finale, it was very almost the perfect ending before he got shot by a Dalek and proceeded to regenerate. He managed to cheat death by pouring the energies into his handy spare hand and then before too long a human Time Lord metacrisis came along which meant that the universe now had two Tenth Doctors for the price of once. Sort of. So why doesn't the Doctor just do this all of the time? Why doesn't he cut off a body part early into each of his incarnations, keep it around in a jar and, when his next regeneration is looming, do the same as the Tenth Doctor did in order to maintain his current look? It would use up one of his regeneration but he's got a new cycle of them now, courtesy of the Time Lords (thanks, boys!), so it wouldn't really be the end of the world. Saying that, the show might not be as exciting if viewers had to deal with someone like Colin Baker for 20+ years...