If you looked very closely (again, the wonders of HD!) you could see the string tension had been lowered considerably so Renee could place her fingers on the strings and “pluck” them; however, the secret was that a mute had been woven through the strings at the top, over the sharp discs, and at the center strip.
I gave Renee a short lesson on hand position and she also insisted on knowing how to mime moving the pedals. She had the lesson videotaped so she could practice! There was a piece of fabric woven through the discs to “mute” the strings. It was actually my playing from the pit that was heard. It’s a tricky little passage with lots of pedal changes!