Feral Ghouls in general, I hate when your going through a dark metro tunnel and all of a sudden you hear that groan its sort of raspy and hoarse and you just know that there are a lot of feral ghouls coming your way. :tops:
With MMM installed, the most dreaded sound becomes a ghoul groan from an area that you just cleared... (ghouls have a chance to reanimate a little while after dying in MMM).
(mutter) I should have taken the time to behead them all...