Stilettos, ready! To keep the audience entertained, the postwar French choreographer Roland Petit resorted to high jinks, low jinks, whatever jinks he could summon. He’s a one-man, nonstop coup de theatre. Petit’s women, long-legged and aloof, aren’t asked to be graceful so much as dangerous and strange: they slither, prance and stamp, opening and closing their knees in insectoid twitches and mechanical jerks. It’s as if they are perched on high-heeled toes. The men must earn advanced degrees in acrobatics (with post-graduate liniment for their abused muscles) to perform Petit’s Cirque de Soleil cartwheels, tumbling, and feats of strength (such as forming a human bridge for the ballerina to stretch out on — at least she doesn’t walk over it in stilettos). These antics were on display in a triple bill mounted by the ever-ebullient English National Ballet, the romping younger sibling of the Royal Ballet, which soberly covets its right of primogeniture.