There is a kind of lubricating fluid called synovial fluid between the joints of fingers. Its function is to prevent any kind of collision between the bones of the junction. Different gases are also saturated in this liquid. When we pierce our fingers, we try to pull the bones apart. This tension increases the space between the junctions and decreases the internal pressure. But when it returns to its former position, the gases at the junction create bubbles, which are called cavitation in the language of science, and these bubbles burst under the pressure and make a noise. Many people think that doing this is harmful. But in 1998, Donald Unger proved that idea wrong. For this research he was awarded the Special Prize in Medicine in 2009.