<P> There were other differences from the novel . Henry Knight was based on Sir Henry Baskerville, but the character Barrymore, a butler in the book, became an Army major . Another character, Fletcher, was original to the episode; the character was based on Bertram Fletcher Robinson, the journalist who assisted Doyle with the novel . In another scene, John notices what appears to be Morse code, but it is unrelated to the case . Moffat named it the funniest instance where the producers take an element from Doyle's works and "do something cheeky with it". The Baskerville base was based on Porton Down military science research centre . While conducting research for the episode, Gatiss learned that artists and scientists made a luminous rabbit, using the green fluorescent protein of a jellyfish, which formed the basis for a side story involving a "glow - in - the - dark" rabbit created at Baskerville by Dr. Stapleton, the mother of the child who wrote to Sherlock at the beginning of the episode requesting that he help her find her missing rabbit . In the episode, it is specified that the spliced - in "GFP gene" that had allowed the rabbit to glow had come from a jellyfish of the species Aequorea victoria . Also, Gatiss suggested the concept of a "mind palace", a memory technique originating in Ancient Greece; the idea came from a book by illusionist Derren Brown . This technique would lead Sherlock to the revelation of the secret H.O.U.N.D. project . </P> <P> Early script drafts had Henry accidentally kill Louise Mortimer, but producers were never satisfied with this development, thinking Henry would have failed if she died . Writers also posited that Henry's father's murder involved revenge after he had an affair, but the producers and Gatiss found it easier to mention he died because he learned of Franklin's experiments with the hallucinogenic gas . The ending also changed; the final scene had originally involved Moriarty entering the Tower of London but that was held back for the following episode . </P> <P> "The Hounds of Baskerville" took around four weeks to film, with shooting mostly taking place throughout May 2011 . Additional scenes were shot later in July and August . Filming on location mostly took place across South Wales, with parts of the episode being shot on location in Dartmoor, even though the producers did not originally intend to do so . The first day took place at a cemetery . The producers were looking for a village in South Wales that was "very English - looking ." Scenes of the fictional "Cross Keys" pub were filmed at the Bush Inn in St Hilary, Vale of Glamorgan . The production team donated £ 500 to the village after filming had finished . In one scene, after Sherlock first witnesses the hound, Sherlock makes deductions about a mother and son from a nearby table . In filming the scene, Cumberbatch has to recall multiple pages of monologue in front of camera, and had to talk faster than he was used to . </P> <P> The scenes at Baskerville were filmed at a number of locations . The exterior was filmed at the gas works by Baverstocks near Llwydcoed in Mid Glamorgan . The labs meanwhile were filmed in two separate locations, one of which was a microchip processing facility . The switch between two locations meant that the crew had to transport a lift set . The scenes in Dewer's Hollow, where the hound was sighted, was filmed near Castell Coch . The reveal scenes in the hollow took two nights to film . At some point filming the scenes were delayed due to rain . The scenes shot in Dartmoor took place in areas such as Haytor and Hound Tor, the latter of which was said to be where the original story was set . </P>

Where was sherlock holmes hound of the baskervilles filmed