Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Story Building

You'll need a small group of people for this creativity exercise. Stand or sit in a circle and have someone start a story. For example: "It was a dark and stormy night..." Go around the circle with each person adding a new sentence.. Try to go around a few times before ending the story. The crazier and more creative the story, the better!
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For more mind exercises: http://www.braingle.com/mind/