Excuse me, how did the erhu part in Walking on the Su Causeway come out? There is a section in the middle of Allegro that is similar to beating the piano tube with a bow?

By the way, this is an ensemble. Are you sure that all the sounds that seem to be made by tapping the piano tube are made by erhu?

Personally, I think the crisp sound is more like the sound of a wooden fish, while the erhu is just plucking the strings with the left hand.