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RIDDLE: I heard this teaser this weekend from a medical student. Apparently, they ask this question to people to know if they are psychopaths. If you can answer it right away, you may have bizarre tendencies. You have all the elements to answer it, you don't have to elaborate complex theories. Ok, here it comes:
A young girl is at her mother's funeral. She meets a young man she had never seen before, but who's there as a part of family. She instantly falls in love with him. A few days after, she kills her sister. Why?
Hint: Remember, you have all the elements of the problem in your hands.

The Correct Answer: http://riddlenow.com/a/271.htm
This Riddle is a cortesy from CoolRiddles Youtube Channel:
   / coolriddles