The Rani's mice

The First Rani created monstrous mice in an experiment on Gallifrey. These mice attacked the Lord President and his cat, injuring the former and completely eating the latter. (TV: The Mark of the Rani) The Time Lord messenger also indicated that he lost his cat in this incident. (AUDIO: The Man Who Wasn't There)

The creation of monstrous mice on Gallifrey dated back to Rassilon, who made horrors with the Loom of Rassilon's Mouse. (PROSE: Happy Endings)

As a tutor in the War in Heaven, the Rani attached an artron emitter to a normal rat, allowing it to fry a gallifreyan cat with its mind. (PROSE: The Taking of Planet 5)