http://www.creepyclassics.com/
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What is the difference between a MONSTER movie  and a HORROR movie?
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The MONSTER movie always ends well. Good prevails. http://www.imdb.com/title/tt0056405/
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The HORROR movie ends badly. Evil wins. http://www.imdb.com/title/tt0119099/

The MONSTER movie is more about naivete - http://www.imdb.com/title/tt0117089/
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The HORROR movie is about sophistication - http://www.imdb.com/title/tt0059646/
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TO BE CONTINUED....

Naive: "Mysterians":

Sophisticated: "Invaders..."