Warning, this post contains plot spoilers...
Next week on Dr Who, the Doctor and his companion will visit an alternative universe in which everyone wears masks of polystyrene and latex, all furniture is made of balsa wood and sugar glass, and all rooms are lit by a strange sort of diffuse lighting that's blue from one side, orange on the other.
When the Doctor and his companion walk into a room, despite the fact that they are completely unknown, the room's existing and legitimate occupants will rush over, and regale the Doctor with intimate details of their pasts. Perhaps their forwardness is understandable - anyone who hasn't told the Doctor or his companion their name, favourite teacher at school, name of their first pet, or their mother's maiden name will be killed within the next half-hour.
Aliens who do not have names, pets, or mothers need not be afraid - they'll be the ones doing the killing.