Mouse

A mouse was a species of mammal native to Earth and possibly other parts of the universe.

On Gallifrey, a mouse was enlarged by the Rani during an experiment. The giant-sized mouse ate the Lord President's pet cat and bit the President himself. (TV: The Mark of the Rani)

In the year 4000, Froyn and Rhynmal intended to test their new long-range teleportation system by sending two lab mice to Mira. These were later exterminated by Daleks. (TV: The Daleks' Master Plan)

The Fourth Doctor called Leela "mouse" after she inhaled helium and it temporarily changed her voice. (TV: The Robots of Death)

On Skaro, Romana II hinted that a determined mouse could move over a barrier the Fourth Doctor was putting on the way of the Daleks. (TV: Destiny of the Daleks)

The Fourth and Tenth Doctors occasionally carried a toy mouse, which he used to distract people. (TV: The Talons of Weng-Chiang, The Doctor's Daughter)

The Doctor claimed that there was a planet which had talking mice. (PROSE: Winner Takes All)

Behind the scenes

 * Jon Pertwee acquired a field mouse as a temporary pet during a break in the location filming for The Mutants at Stone House Farm in Frindsbury, Kent. He named the mouse Solos, after the planet featured in the story.