Panther

s were a type of felid mammal the Third Doctor and the Brigadier once encountered at a zoo, early in the Third Doctor's life. Normally fierce, this was be as docile as an ordinary house cat. This odd behaviour made the Doctor and UNIT suspicious of nearby activities. (TVC: The Arkwood Experiments)

The Second Doctor, John and Gillian also encountered a panther. Once, while visiting New York City, the trio went to a zoo and ran into a panther that was being controlled by a misguided human scientist. The Doctor was only able to avert the panther's unnaturally aggressive attack by using acid against it. (TVC: The Monsters from the Past)