Every recorder player knows this: you must oil your instrument regularly. This is because the instrument itself is at the mercy of all nasty things: your spit, dirt, and other natural conditions. You would not want those to build up on your instrument. So that’s where the oil comes in. Plastic recorders don’t need much oil, but wooden ones do, and regularly so. Oiling keeps the sound beautiful and the recorder itself responsive to your playing. Without oil, the wood will swell and dry, affecting the sound in a bad way.