The real uses...

As the Mridangam Vidwan was playing inside the sound proofed chamber, the Violinist sitting outside followed it from the way the fingers moved. That is when the sweeper lady came in. She gestured to the mridangam player inside and told her apprentice, something to this effect: "Do you know what he is doing? If you do that, you get very nice callous on your fingers." The violinist smiled with compassion and kept on watching the player.