Rodents Of Unusual Size are giant rat-like creatures that Westley and Buttercup encounter in the Fire Swamp. These beasts eat practically anything, especially living things, including humans. They are dangerous, but only attack if they smell blood or outnumber their opponent.

Westley and Buttercup's encounter with the (in the film) was striking. The rodent's presence is made known through a sinister foreshadowing before it leaps into the scene, attacking Westley. Westley immediately engages combat with the rodent, and Buttercup is horrified—standing on the side. Westley eventually defeats and kills the rodent after a bloody battle.