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. (DW: 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. (DW: The Daleks' Master Plan)

The Fourth Doctor jokingly compared Leela to a mouse after inhaling helium temporarily changed her voice. (DW: The Robots of Death)

The Doctor occasionally carried a toy mouse. (DW: The Talons of Weng-Chiang, The Doctor's Daughter)

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

Other references

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