Brain Slugs are small, one-eyed, vaguely sluglike aliens which attach themselves to the heads of sentient beings to control them. Brain slugs apparently use this as a method of trapping more "prey", since those beings under brain slug control are driven by the desire to place brain slugs on other beings. It is hinted that the host under the brain slug's control retains awareness of their condition, which Hermes referred to as a "nightmare". The brain slug can be seen in numerous episodes, normally attached to Hermes. For a short time, Fry had one attached, but according to the professor, it "starved to death" due to Fry's low intelligence.