Boggart question
I've just been re-reading the third book, and in the chapter with the Boggart, Lupin says at one point that nobody knows what a Boggart looks like in its natural form (since it instantly transforms when in the presence of people). But I'm sure I can remember a part from a later book where somebody asks Moody to check if there's a Boggart in another room, which he then does so using his magical eye (without even leaving the room they're in). So shouldn't that mean Moody knows what Boggarts really look like and can tell other people?
http://www.youtube.com/watch?v=L_jWHffIx5E&ob=av2e