He decided he would ‘play’ this on my keyboard and requested me to sing (so found me a random sheet of music with some words on it). This was an… interesting experience. :-)
Unfortunately, on Sunday afternoon I came back from a trip to the loo to find that smallclanger had made up a game which involved spooning water out of a container, that the most convenient horizontal surface on which to place the vessels was the keys of my keyboard, and that he was busy trying to wipe up an accidental spill. "Look, it still works!", says he, turning it on and playing a few notes. Once the water had soaked in, though (and there was rather more than I first thought), half a dozen of the keys played themselves every time the keyboard was switched on.
I am kind of hoping that it will get better as it dries out, but if it doesn't then, like Gabriel Gray, I may be compelled to take it apart in order to understand how it works.