A Denevan neural parasite was roughly disc-shaped, about thirty centimeters in diameter and two to four centimeters in height. The edges were thin and yellowish; towards the center, the creature was thicker and redder. Occasionally, they pulsated. Parasites had no detectable external or internal organs. Spock described a parasite as "resembling, more than anything, a gigantic brain cell." Looking -- and moving -- like a half-digested Frisbee, these creatures are part of a large organism that takes over humans' nervous systems and forces them to infect other planets, kind of like Borg without the fashion sense. (This is also the episode where we learn that Spock has nictitating membranes. That doesn't have much to do with the monster. It's just creepy.)Denevan neural parasites were capable of clumsy flight. They attacked by making physical contact with a target and stinging it as does a bee. The stinger injected a strand of tissue that infiltrated the victim's nervous system very rapidly, entwining about the nerves. Leonard McCoy described this entwining as "far, far too involved for conventional surgery to remove." Once the parasite infiltrated a host, it pressured the host to obey its commands by inflicting enormous pain. There seemed to be some level of pain even when the host obeyed, but the creature could increase the pain it inflicted to bring an uncooperative host to heel. Exactly how the creature communicated its desires is unclear, but that it could do so is evident: Spock, while infected, attempted to land the Enterprise on Deneva, despite the fact that (as he knew) this was impossible. Later, he was able to end the pain through mental discipline and convince the crew to let him collect one of the parasites to run tests on. Eventually, this continuous painful stimulation could have led to insanity and death. Infected victims cooperated in working towards the parasites's objectives. This, and their enormous resistance to harm, led Spock to theorize that all of the parasites were parts of a single organism. How the parts communicated without a physical connection was not made clear. The parasites were so alien that Spock also theorized their origin was a place where different physical laws applied, outside of the Milky Way Galaxy. Instinct: Destroy

• Infects
• Enslaves with pain
• Sunlight kills
• Magical healing kills