4 ideas
Dr. Valentine Pilman argues that the aliens' Visit was not contact with humanity but a stopover, like travellers picnicking by a road and driving off, leaving litter behind. The Zone's artefacts are their discarded rubbish, and humans are the ants and birds that pick through it afterwards without understanding any of it. The lens changes the question 'what did they want from us?' into the more deflating recognition that they may not have noticed us at all.
Humanity puts Zone artefacts to work, such as the 'so-so' perpetual batteries, while having no model of how they function. The novel argues that this use without understanding is closer to a savage using a microscope as a hammer than to science. The same objects also generate unforeseen harms, including lethal traps, mutated children and mysterious deaths. Practical exploitation proceeds anyway, driven by profit and military interest, and outpaces any comprehension of the risks.
Stalker Redrick Schuhart guides young Arthur Burbridge deep into the Zone to reach the Golden Sphere, a wish-granting artefact. He knowingly lets Arthur run ahead to die in the 'meat grinder' trap, because a life must be spent to clear the path. At the Sphere, Red finds he cannot articulate any wish of his own, and he ends up repeating Arthur's last words: 'HAPPINESS FOR EVERYBODY, FREE, AND LET NO ONE BE FORGOTTEN!'
The Visit's effects are not confined to the Zone's geography. Emigrants from the Harmont region bring abnormal consequences wherever they go, including clustered disasters and elevated death rates in their new towns. Stalkers' children are also born altered, as with Red's daughter Monkey, who is covered in fur and slowly loses her humanity. Exposure to an incomprehensible system turns the exposed people themselves into carriers, so quarantining the place does not contain the effect.