In the most famous first lines of the Kafka's tale "The Metamorphosis", written in the year 1912 and published in Leipzig 1915 by Kurt Wolf Verlag, we read that after a night of troubled dreams one morning at the awakening Gregor Samsa found himself in his own bed tranformed into an «ungeheueren Ungeziefer»: «enormous (unclear) vermin». At the Kafka's age the word «Ungeziefer» was used in the ordinary speech in the figurative sense of «scum, rabble». In the tale this figurative sense becomes «blood and flesh» of a real «Ungeziefer» through the nocturnal metamorphosis of the travelling salesman Gregor Samsa. The «human» is so reversed into an «animal body with its animal sensations» in order to investigate the «shadow line» or the threshold between humanity and animality, cruelty and creatural pity. Devoted to the tale's first part, this essay essentially consists in an analys into the narrative and linguistic means by which a strictly methonimical writing, i. e. a physical precision as it was expected by the «flaubertian» canon, the tale forms an universe of allegorical meaning.