Very large, extremely odd creatures which exist solely within the confines of the Fire Swamp in the 1987 Rob Reiner film "The Princess Bride." Shortly after being rescued from an evil patch of quicksand by the brave and valiant Wesley, the duo faces an encounter with one of these miserable creatures when one springs on Wesley from the dark confines of the swamp. This happens in response to the following dialogue between Buttercup and Wesley, as they lie comforting each other after their ordeal with the quicksand:
Buttercup: What about ROUS-es?
Wesley: Rodents Of Unusual Size? I don't believe they exist.
What ensues is a vicious battle between our hero and what appears to be either a very, very large rat (true to the name) or perhaps an incarnation of former U.S. Congressperson Newt Gingrich. Wesley, of course, wins easily, stabbing the vile creature multiple times in its torso after throwing it very cleverly onto a convenient burst of flame, setting it on fire (tip: it is a very comical thing to see, a giant rat burning alive, that is). And you can bet that nary a ROUS dared to come near them after seeing THAT happen to one of their own.