They could not close the windows behind them, so in some way the windows close themselves.
“I went to one window and took out the nail. It was very strong. I tried to open the window, but I could not. Then I knew that there must be a hidden spring in the window. I searched carefully and found it.
“So a person could close the window after he left through it. But, of course, he could not put back the nail. So I looked at the other window. It had a similar spring, and the nail in it seemed as strong as the other one.
