"Second Variety" is a science fiction novelette by American writer Philip K. Dick, first published in Space Science Fiction magazine, in May 1953. Set in a world where war between the Soviet Union and United Nations has reduced most of the world to a barren wasteland, the story concerns the discovery, by the few remaining soldiers left, that self-replicating robots originally built to assassinate Soviet agents have gained sentience and are now plotting against both sides. It is one of many stories by Dick to examine the implications of nuclear war, particularly after it has destroyed much or all of the planet. The story was adapted into the movie Screamers in 1995. "Second Variety" occurs in the aftermath of an extensive nuclear war between the Soviet Union (sometimes referred to as Russia) and the United Nations. Early Soviet victories forced the North American government and production to flee to a Moon base, leaving the majority of their troops behind. To counter the almost complete Soviet victory, U.N. technicians develop robots, nicknamed "claws" -the basic models are "a churning sphere of blades and metal" that ambush their unsuspecting victims "spinning, creeping, shaking themselves up suddenly from the gray ash and darting toward... [any warm body]." U.N. forces are protected from the claws by a special radiation-emitting wrist tab. Within six years, the sophisticated and independent claws have destroyed the Soviet forces, repairing and redesigning themselves in underground automated factories run without any human oversight. wikipedia.org)