 Why does Paul think aliens are watching Earth?
The poorest will try to sell you anything from a shoeshine to their not very lily-white bodies, and the richest will avoid your eyes, afraid you might try to sell them something. As a result of them the permanent population includes smugglers and black-marketeers, fugitives from justice and international con men, espionage and counter-espionage agents, homosexuals, nymphomaniacs, alcoholics, drug addicts, displaced persons, ex-royalty, and subversives of every flavor. Local law limits the activities of few of these. Paul said, "What ever happened to those poxy flying saucers?"
 The aliens are watching Earth's civilization go through wars and struggles as a form of amusement.
 The aliens are watching Earth's civilization go through wars and struggles as a form of amusement.  They want to invite Earth to join the Galactic League of civilized planets.  Man has invented the H-Bomb. The aliens are scared.  The aliens are preparing to harvest humans as a food source.