In Order of the Phoenix, Mad-Eye Moody identifies a Boggart for Molly Weasley.
"We've been wanting to ask you for ages -- could you have a look in the writing desk in the drawing room and tell us what's inside it? We haven't wanted to open it just in case it's something really nasty."
"No problem, Molly."
Moody's electric-blue eye swiveled upward and stared fixedly through the ceiling of the kitchen.
"Drawing room . . ." he growled, as the pupil contracted. "Desk in the corner? Yeah, I see it. . . .Yeah, it's a boggart. . . .Want me to go up and get rid of it, Molly?"
(Order of the Phoenix - Page 169 - US Hardcover)
Prisoner of Azkaban tells us that no one knows the natural appearance of a boggart. However, would Moody's magical eye allow him to see a boggart in its natural state? Or would he have just seen his own boggart, the thing that scares him the most?