Some artists need flash bombs to make an impression on stage. Some need giant screens. Some need to run around like hyperactive toddlers. All Grace Jones needed was a hula hoop – not the delicious potato snack, but the plastic ring. For the ten minutes or so of ‘Slave to the Rhythm’ that ended her set on a balmy evening in the courtyard of Hampton Court Palace, she languidly rotated the ring around her hips, all while she strode across the stage, then climbed a set of stairs.