Once I was scheduled to play the Waldstein Sonata for a musical society. Preceding me was a string quartet. When they finished, I was called and after some applause I sat down at the grand piano. The keyboard lid was closed and looked a little unusual. When I opened the lid, to my horror, there appeared a double keyboard, like that on an organ. I started playing, but couldn't concentrate - I kept looking at the keys immediately above the ones I was playing. It made my head spin. It wasn't long before I got completely lost. I apologized, explained that I coldn't play this piano, and left. Very embarrassing..........