Happy Jack in "What Was The Matter With Farmer Brown's Boy?"

But when they finally ventured on to the sill and, as they helped themselves to nuts, saw the smile in his eyes, though he did not smile with his mouth at all, they knew that it was he, and that he was glad that they had called. Then they were glad too.

But what was the matter with Farmer Brown's boy? Happy Jack puzzled over it all the rest of the day, and then gave it up.