I have a Lurker in my house. He is 14, my eldest son, and he is totally intrigued by the fact that his mother is taking piano lessons along with him. The younger ones are not taking piano during the summer, but John Mark wanted to keep working on Pachelbel's Canon with his teacher, Miss Kim. On lesson days, he goes first and I follow. And he listens.
During my first lesson, he hid in the big easy chair and peered around the edge. He made some sort of noise once and irritably I asked, "Would you please leave?" He didn't, and I didn't press the issue. I told John later that John Mark was eavesdropping on my lessons, and my husband said, "Well, he's getting two lessons for the price of one!" And I suppose he is. He is fascinated. He continues to eavesdrop, and I let him, hoping he is learning to become a better musician by watching and listening to my example.
It makes me wonder what else he is learning.