This Princess Bride t-shirt shows a R. O. U. S. in the dreaded Fire Swamp. The shirt reads Beware Rodents Of Unusual Size. 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.