Imagine a computer programming class. A young man and a young woman are facing each other working at computers. The computers, of course, sit back to back. A few minutes into the class, the young woman leaves the room; whereupon the young man reaches between their computers and switches the inputs for the keyboards. The young woman comes back and starts typing. Immediately gets a distressed look on her face. She calls the teacher over and explains that no matter what she types, nothing happens.

The teacher then tries with the same result. By this time the young man is hiding behind his monitor and quaking red-faced. He types, "Leave me alone!" The teacher and the young woman both jump back from the computer screen, silenced.

"What on earth???" the teacher blubbers. Then on the screen app…