Rule # 1 for aspiring conductors: wear comfortable shoes.
Maestro Daniel Barenboim, a most pragmatic man, last night on the podium realized that the powah of Wagner had badly torn one of his shoes. So he came back for Act II wearing a new, borrowed pair of black shoes. That were too tight and uncomfortable, and you don't want to conduct an opera that long in uncomfortable shoes.
So he took them off, for the amusement of the orchestra, and led Act II and III of la prima at la Scala in his socks (one hopes they weren't holes in them).
So much for dress codes.