In dance, it’s usually the moment the boys start fighting that challenges your suspension of disbelief. Synchronised fencing (MacMillan’s Romeo and Juliet), unison goosestepping (Grigorovich’s Spartacus), even the Sharks and Jets in Robbins’s West Side Story, are formation set-pieces designed to arouse us. Last year there was a bunch of ballets made by British choreographers to mark the first world war centenary, which artfully focused on sorrow.