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Flash mob rocks Sydney Opera House

According to Wikipedia: A flash mob (or flashmob) is a large group of people who assemble suddenly in a public place, perform an unusual and pointless act for a brief time, then disperse. The term flash mob is generally applied only to gatherings organized via telecommunications, social media, or viral emails.The term is generally not applied to events organized by public relations firms, protests, and publicity stunts. See the report from Ten News.