Piano Sonata

You are giving a piano lesson to Megan Fiore and Sapphire Lapiedra. They take turns to show you how they play the piano, but at some point, they start to compete between them and to annoy the other by touching the keys, correcting them… They ask for your opinion about which one plays better, but suddenly one of them says: actually professor, there is something that we both know how to play very well.