I learned this game at the 2005 OCA Conference, at the "No Equipment, No Planning Time, No Problem" session facilitated by Matt Barr.
Have a group of 20 or more people line up face to face (10 on one side, facing 10 on the other). Ask a question and give the people facing each other 30 seconds to discuss their answers. When this is completed, everybody in line A shifts one position and you provide the group with a new question.
Some examples might include:
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