Infestation

Infestation is one of the defining traits of the Zerg in StarCraft, alongside biological adaptation and genetic assimilation. Some Zerg units infest enemies with parasites, from ones that let the Zerg see what an enemy unit sees to ones that spawn Zerg inside it. The Zerg can also infest some Terran buildings to produce infested Terrans, humans genetically mutated into human-Zerg hybrids. In the story Sarah Kerrigan is infested and becomes the Queen of Blades, and a Xel'Naga artifact later de-infests her.