Re: 7X11 The Crimson Horror(Grading/Discussion)(SPOILERS
In this episode, we learn that the trio discovered the whereabouts of the Doctor after developing an image which revealed a mirror image of him on the iris of a deceased man. This is bogus science, but I don't question it because this is Doctor Who, and weird science is an essential element of the series.
It was specifically stated that -normally- it wouldn't be possible, but that the chemicals they were being dipped into caused enough of a change in the tissues to allow it.
"There is no reason why good cannot triumph as often as evil. The triumph of anything is a matter of organization. If there are such things as angels, I hope that they are organized along the lines of the Maffia." - Winston Niles Rumfoord.