As part of our experiments we realized that jello and fruit, which contain a lot of water, are conductive. Embedded in each jello/fruit key is a sterling silver pin (food safe) connected to an Arduino microcontroller underneath the piano’s base. Below the piano’s case is another sterling silver pin. With this setup, the JelTone can either be played with a metal utensil connected to the Arduino, gloves enhanced with conductive thread, or bare hands by touching both a key and the piano’s case.
Technical info at Thingiverse.