DarkWarning
From hugolib.h:
MovePlayer calls DarkWarning when there is no light source in the new location; replace it with a new DarkWarning routine for a more elaborate response, such as the possible demise of the player
Really, I think that says it best.
The code
routine DarkWarning
{
print CThe(player); " stumble"; MatchSubject(player); \
" around in the dark."
}