About two-dozen local members of Sweet Adelines International Singers stripped off jackets and sweaters to reveal matching blue t-shirts and began clapping and singing. A crowd of onlookers gathered for the performance — which lasted about 10 minutes — as the group shimmied and performed songs from their repetoire, including Duke Ellington's classic "It Don't Mean a Thing (If It Ain't Got That Swing)".
Their shirts were emblazoned with the words "Flash Mob Attack!" and included place — Bellevue Square — and today's date, Nov. 12, 2011.
According to Wikipedia, A flash mob is a group of people who assemble suddenly in a public place, perform an unusual and sometimes seemingly pointless act for a brief time, then disperse, often for the purposes of entertainment, satire, artistic expression.
Sweet Adelines International Singers describe themsleves as a worldwide, non-profit organization of women singers committed to advancing the musical art form of barbershop harmony through education and performances. "Harmonize the World" is the organization's motto.