Chapter 39 in the Unlikely Attack Scenario Handbook
What are these things, and why are they attacking me?
C.H.U.D.—— short for Cannibalistic Humanoid Underground Dwellers
-are homeless people who have been mutated by radioactive waste into flesh-eating maniacs. They were immortalized in the 1984 film C.H.U.D.
The C.H.U.D. are attacking you because you have fallen into an open New York City manhole, and they long for the taste of your still-living flesh. It is like chocolate covered almonds to them.
How do I stop a CHUD?
First of all, we recognize that you're under considerable attack-related stress right now, and grammar concerns are probably not foremost on your mind. However, the editors of this publication ask that you please try to punctuate the term C.H.U.D. It is an acronym.
Additionally, as the D in C.H.U.D. stands for 'dwellers', the term C.H.U.D. should be seen as the plural form.
What' the singular form?
The feature film is unclear on this point, but given that C.H.U.D. hunt in packs, it is plausible to assume there isn't one. You will be always be attacked and killed by multiple C.H.U.D. In the event that you wish to refer to one mutated zombie cannibal vagrant, the editors of this publication recommend keeping the plural form.