I played this piece last year called 'Quadrivial' by european composer Michel Van Der Aa. It was for flute, violin, cello and piano, and i got to bow the strings of the piano (with bow hair), not quite as much as in that video.. i only had about maybe 10 strings to bow, at first i couldnt work out how to make the sound, but then i thought, err put some rosin on it.. so now some of the strings have rosin all over them lol. it makes a really interesting and haunting sound