He smiles as Patty leans over him and asks, "What is that you're playing, Schroeder?" Charlie Brown stands nearby and says, "I don't think he knows..."
Patty turns to him, points at Schroeder, and replies, "What do you mean?! He's playing it, isn't he?"
Schroeder hides his face in embarassment as Patty looks at him, and Charlie Brown replies, "Sure, but he can't read the title!"