Brian Eastman, the show's producer, saw a three-legged dog in Regent's Park while he was working on the script for this episode. "A few weeks later, the dog was the star of the script", he commented. Brian had hoped to use the same dog for the show, but he never found it again. The search was on for a replacement, and luckily a Jack Russell with a missing leg, who really is called 'Holly', was found and signed up. In real life, Holly is the boss of a pub near Oxford.