The Water Piano is a classic electronics project. The user spreads a thin layer of water on the tabletop and places a lead from H1 in the water. While holding the other lead (H2), the user touches the water with their finger. The further they contact the water from H1, the higher the resistance of the body+water combination, resulting in a lower frequency tone from the 555. By sliding their finger along the water the user can create beautiful music.

Well, some users can create beautiful music... mostly it is just joyous noise. :-)

The extra 0.130" holes in the board are for use as either mounting points or as strain reliefs for the wires. The most common point of failure on the circuit is wire damage due to metal fatigue... always use stranded wire and ensure the wires are strain relieved to create a durable product.

This circuit certainly isn't my design... it has been around for decades, but this is the board I made for my students. More detail on how it works (including instructions on how to breadboard it, and simulate it on Falstad's Circuit Simulator) at https://botshop.wordpress.com/2017/11/02/the-water-piano/