How could he know that song?
His mother had strictly forbidden him to show it to anyone, and he had only read it aloud at home.

How could a stranger hear about it?
"You can say in your new song that Mr.Castle-Steward and Mr.Trius are two persons and not one; you can see that yourself," Maezli declared aloud.
Kurt then suddenly understood that his impudent small sister had probably been the informer and he did not know what to answer.
But Leonore helped him over his embarrassment by continuing, "This is Lippo, Uncle, who has asked me to live with him when he is grown up.
Isn't he a wonderful friend, Uncle?
He knew I had no home." "You have quite marvellous friends, Leonore," said the Baron; "they must visit you very often, if Mrs.Maxa will allow it." "Gladly, and I know that their happiness will be yours, too, when you see them all wandering through the house and garden." "Yes, all of us, and Salo, too," Leonore exclaimed.

"Do you think Salo will soon be here, Uncle ?" Apollonie had approached the lively group under the pine tree, and as there happened to be a suitable pause, she announced that dinner was ready.
"I really ought to invite my dear friend, Mrs.Maxa, to come to the table _with me_; I shall ask, however, who is going to take me ?" said the Baron.
All the children immediately cried, "I," "I," "I," "I," "I," "I," and hands caught hold of the back and both sides of the Baron's chair.
"I am driving in a coach and six to-day! How things have changed for me!" the gentleman said smilingly.

The meal Apollonie had planned was a great success and the open air on the terrace added to the children's enjoyment.
When the fruit course, which consisted of yellow plums, was eaten, the Baron gave the young birds, as he called the children, permission to fly freely about.

It seemed to crown all the preceding pleasures to be able to roam without restraint in the woods and meadows.