"Found in virtually every psychology textbook in the world, the two monsters in this illusion are in fact the same size. Your brain automatically adjusts images that it perceives to be distant in order to compensate for the fact that they are larger than they seem."
A list of Doctor Who minisodes you may have missed :) - The interactive one where you become The Doctor's companion is awesome! When he was sending me back I was like "Wait. No. I don't want to go back" :(