This Princess Bride t-shirt features a black and white image of a Rodent Of Unusual Size from the Fire Swamp. The shirt reads R. O. U. S. They do exist! Rodents Of Unusual Size are giant rat-like creatures that Westley and Buttercup encountered in the Fire Swamp. These beasts eat practically anything, especially living things, including humans. Westley and Buttercup encountered a R. O. U. S., which Westley defeated and killed in the Fire Swamp.