The sale of a Banksy painting for $1.4 million, the highest-ever paid for the British street artist’s solo work, was the perfect finale for Sotheby’s successful “Frieze Week” evening contemporary art auction on October 5, 2018. But before the auctioneers had time to celebrate, an alarm sounded and then, to everyone’s dismay, the artwork began to self-shred while sliding down the frame.