Difficulty: Easy

Professor Lipshultz is showing off his new inventions to a prospective investor. He tells the investor that he had developed four machines that will allow scientists to study the motion of gas molecules. His explanation of how the machines work together goes as follows:

“The first unit will take in any gas and completely dry it, removing all traces of water. Right now it is removing water vapor from air … and now you can see the ‘DRY’ light has come on.

“The second unit removes all but one molecule from the chamber. There you see the ‘READY’ light, indicating that only a single molecule remains.

“The third unit analyzes the contents of the chamber, determining exactly what chemicals are in the chamber, and in what quantity. And as you can see on the screen, the unit indicates ‘Air: 1 molecule.’

“The final machine will trace the path that the molecule takes as it bounces around the chamber. The path is represented by the lines on this computer screen.”

“I'm sorry,” said the investor, “but you're obviously lying to me. I can accept the fact that three of the four machines could work as you say, but one of them is obviously a fake.”

Which machine was the fake?