nasal demons

nasal demons n.  Recognized shorthand on the Usenet group
   comp.std.c for any unexpected behavior of a C compiler on
   encountering an undefined construct.  During a discussion on that
   group in early 1992, a regular remarked "When the compiler
   encounters [a given undefined construct] it is legal for it to make
   demons fly out of your nose" (the implication is that the compiler
   may choose any arbitrarily bizarre way to interpret the code
   without violating the ANSI C standard).  Someone else followed up
   with a reference to "nasal demons", which quickly became
   established.