The C.H.U.D.s (or Cannibalistic Humanoid Underground Dwellers) were from the 1984 film of the same name. They are beings that were once human, but have been mutated into hideous, flesh-eating creatures by radioactive, chemical toxic waste. They prey on the homeless who live in the underground tunnels. Given that they killed all of the said homeless people, the recent drop in the underground population makes them resort to coming to the surface through sewer manholes in order to feed. Anyway, it turns out that the NRC (Nuclear Regulatory Commission) were directly responsible for this slaughter due to the fact that they have been illegally and secretly dumping toxic waste and the protagonists are left with a corporate foe as well as a cannibalistic one.