In the DVD commentary for this episode, writer Steven Moffat reveals that up until a very late stage, the nanogenes in this story were called "nanites". However, script editor Helen Raynor decided this name sounded too much like similar nanotechnological devices in "". Moffat had first used the line "Life is just nature's way of keeping meat fresh" in the second series of his 1990s sitcom "Joking Apart". He reused it here as he thought it was a good line, but laments that people quote lines from this episode instead of that one. The Chula ships are named after Chula, an Indian/Bangladeshi fusion restaurant in Hammersmith, London where the writers celebrated and discussed their briefs on the scripts they were to write for the season after being commissioned by Russell T Davies.