I have a question...

I. Don't. Know.

Nazis are kind of scary, but old, elderly, French Nazi sympathisers are really THAT scary.

It's not like one of the priests perform an exorcism during the movie.

Maybe because it was truly a horror to watch?

Where did you get that it's categorized as a "horror"(unless its since been changed as this is an old thread)?
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This movie is billed as a 'drama' not a horror movie. There's nothing in this movie that would put it in the horror category.