Aside from evolution, Charles Darwin also studied earthworms. He was fascinated with earthworms and their behavior. He wanted to see how they would react to different stimuli. The part where he played the piano was when he wanted to test their hearing.
In this experiment he tried to blow a whistle, let his son play a bassoon, and even tried shouting at them but it was observed that the earthworm showed no reaction. He tried to play a piano beside the earthworm and still no response. He then noticed that if you put them on top of the piano, they reacted, and thus he concluded that earthworms are sensitive to vibrations.
