 Why does Paul think aliens are watching Earth?
They're all weirdies of one kind or another. The Place de France is the town's hub. King-size sidewalk cafes occupy three of the strategic corners on the Place de France. In native costume you'll see Berber and Rif, Arab and Blue Man, and occasionally a Senegalese from further south. In European dress you'll see Japs and Chinese, Hindus and Turks, Levantines and Filipinos, North Americans and South Americans, and, of course, even Europeans—from both sides of the Curtain. 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?" A French girl went by with a poodle so finely clipped as to look as though it'd been shaven. "You know, what everybody was seeing a few years ago. Tapas at the Cafe de Paris are apt to be potato salad, a few anchovies, olives, and possibly some cheese.
 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.