This consists of a laser pointing at a light sensor across a gap. The light sensor is connected to a speaker, so if you move an object like a piece of mesh across the gap it will block the light many times a second you produce sound.
You can experiment with moving different objects with different patterns of holes, such as sieves, fabrics, combs etc, at different speeds to see what sounds they make.
You can also make acetates with sound patterns printed onto them and produce more complex sounds. This is how sound was stored on film until digital audio was introduced.