Cat flap

A cat flap was a small entrance built into a door. It allowed a cat to enter and exit a building easily. Rose Tyler's flat on the Powell Estate had a cat flap. Jackie Tyler bolted it down to stop stray cats from coming in. The Ninth Doctor followed a signal to the flat and inspected the flap. In the process he knocked the bolts from it. An amputated Auton arm entered through the cat flap shortly afterwards in an attempt to kill the Doctor and Rose. (TV: Rose)

Roger Davey's house had a cat flap. When he was taking the Adipose Pills, the Adipose that was created left his house via the cat flap. (TV: Partners in Crime)