Leo and I were on the airplane and, since his feet exactly reach the seat in front of him, he kept kicking the seat. I told him someone was sitting in that seat and asked him several times to stop and he kept forgetting, of course. Finally I explained to him, "Do you know what that feels like? It feels like this!" And I started shaking his seat really hard. He squealed in laughter, "Do it again! Do it more!"