main narrative was inspired by Rachel Carson's 1962 environmental science book Silent Spring, the first major documentation on human impact on the environment. The fictional insecticide featured in the story, DN6, was inspired by incidents described by Carson regarding the impact of DDT on insects. Writer Mark Wilson wrote in 2017 that the story aired during a time where environmental awareness was beginning to develop among the British public. Whitaker commissioned Marks for the serial in May 1964, then titled The Planet of Giants. Mervyn Pinfield was assigned to direct the serial. Filming The special effect inserts of a cat were filmed on 30 July 1964 using silent 35mm film, with sound added later during a studio recording. The show's regular cast—Hartnell, Russell, Hill, and Ford—filmed the sequences in which they appeared alongside giant props; the effect was achieved by recording the actors through glass and reflecting the object onto a half-silvered mirror. The footage was later deemed unsatisfactory, and the scenes were re-shot on 13 August. Rehearsals for the first episode took place on 17 August at the London Transport Assembly Rooms, across the road from the BBC Television Centre. Weekly recording for the serial began on 21 August at the Television Centre, Studio 4. Due to Pinfield's other commitments, the fourth and final episode was directed by Douglas Camfield, who had worked as a production assistant to Waris Hussein during the show's first season. The final episode was recorded on 11 September. Post-production Planet of Giants is the first Doctor Who serial to feature the work of incidental music composer Dudley Simpson, who first recorded on 14 August 1964. On 19 October 1964, head of serials Donald Wilson decided to reduce the four-part serial to three episodes, as it was felt to be an unsatisfactory opening to the show's second season; he preferred to open the season with the following serial, The Dalek Invasion of Earth, but narrative events prevented the change. The two 24-minute episodes were edited together into a single 25-minute episode from 29 October–2 November to form a faster-paced climax featuring the main characters. Camfield was credited for the final episode. Reception Broadcast and ratings Planet of Giants was considered a strong debut to the second season, receiving 8.4 million viewers for the first two episodes and 8.9 million for the third. An Audience Research Report on the first episode indicated that the show had