I wrote about Serkin and his gigantic encore, here are the details:

   1921, Serkin gave a Bach concert with Busch (violin). At the end,
   Busch pushed him out, telling him to play an encore.  "What shall
   I play?" asked Serkin.  "The Goldberg Variations," answered Busch,
   jokingly.  Serkin took him seriously.  He says that when he finished,
   there were only four people in the audience -- Busch, Schnabel, Alfred
   Einstein, and himself."  From 'The Great Pianist's: From Mozart to
   the Present', Schonberg, pp. 452

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