Open the Window

One night an old professor was at a hotel in the same room with another, man. It was so hot that he could not sleep. So he asked the man to open the window.

“I cannot open it,” said the man.

“Then break the glass,” said the professor. The man did so, and they slept very well.

In the morning they looked round and cried, “But we have broken the glass of the bookcase!”