Their presence is signaled by a foggy, radioactive mist cloud and an intense cold. Though nothing is known about the creatures' origin and motives, Professor Crevett theorizes that they might have come from a dying planet, seeking to colonize other worlds; he also acknowledges their preference for mountains as indicative of different atmospheric requirements, and believes the cold foggy cloud represents the aliens' attempt to reproduce their own environment; possibly even the beginning of an attempt to "xenoform" Earth.