As a crowd of about 200 watched, "Anonymous 9000" spoke on a big screen, his mask and white gloves lending theatrics even as he talked soberly about the inner workings of a movement that has alternately inspired, intimidated and baffled the Web.
There are three bony loops in your inner ear, called semicircular canals, arranged perpendicular to each other to measure movement in three dimensions.
Former minister Peter Kilfoyle has said Mr Mandelson's return to the "inner circles" of government would be "unpalatable" to many people in the Labour movement and in public life generally.