The Furies, or the Little Sisters of Perpetual Velocity, are bird-like humanoids from Ephebe. They are employed by Lady Margolotta to pursue Nutt to prevent any primeval instinct from escaping and causing Nutt to hurt anyone. They often say Awk! and have been described as "chicken"-like by a passenger on a bus to Sto Lat and back to Ankh-Morpork. Here, three of them are seen, though earlier in the book Nutt mentions the "Little Sisters", presumably these are the young and are described as chicks.
Although not appearing in-story until Unseen Academicals, furies are listed as one of several creatures a Tsortean sergeant in Eric had spent his fifty-year military career fighting. As the sergeant in question lived some thousands of years before the Century of the Fruitbat, it's anyone's guess whether the other Greek-flavored monsters (harpies, cyclopses) he'd battled are still extant.
In Greek mythology the Erinýes (Ἐρινύες, pl. of Ἐρινύς, Erinýs; lit. "the angry ones") or Eumenídes (Εὐμενίδες, pl. of Εὐμενίς; lit. "the gracious ones" or sometimes "the kindly ones") or Furies in Roman mythology were female, chthonic deities of vengeance or supernatural personifications of the anger of the dead. So not really what you want looking over you...