Which of Brothers’ Grimm fairy tales is considered the darkest and least meant for children?

I need to choose a story to animate for my final project and I know I want to use one of Brothers’ Grimm fairy tales. With few exceptions, like Simpsons or Futoram, animation is still largely considered to be for children and I want to address older audience. So I am looking for an interesting, but dark and “not for kids” story.
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What about “The Story of the Youth Who Went Forth to Learn What Fear Is”?
It’s VERY dark, and filled with spooky corpses and coffins … it’s way too scary for kids; they must’ve been much tougher hundreds of years ago.
http://en.wikipedia.org/wiki/The_Story_of_the_Youth_Who_Went_Forth_to_Learn_What_Fear_Was
Gingerbread Man–where the witch cooks the little kids
Little Red Riding Hood (was that the name?) one with the wolf
Rumplestiltzen–one where guy fell asleep