Pig-rat

A pig-rat was a kind of non-sentient rat which lived on Gallifrey. They could eat through Time Lord flesh, at least according to a threat Janartis once levelled against Romana II. Indeed, Romana's home of Heartshaven was once overrun by them. (BFG: Panacea)

Pig-rats once swarmed a medical station in the Outlands to which Leela had to go during the civil war between Romana II and Pandora. (BFG: Fractures)