As Mrs Gillyflower launches the rocket, she sings the line "I'll labour night and day to be a pilgrim." This is from Percy Dearmer's version of John Bunyan's hymn, 'To Be a Pilgrim' or 'He who would valiant be'. Furthermore, Mrs Gillyflower sings it to the melody 'Monks Gate', to which the words were set by composer Ralph Vaughan Williams.
"Thomas Thomas" gives directions like a GPS. Tom Tom is a manufacturer of GPS devices.
This is the 100th episode since the return of Doctor Who in 2005.
The front door of Madame Vastra's house is painted a glossy version of TARDIS blue.
At the time, Mark Gatiss and Rachael Stirling were appearing in a stage production of The Recruiting Officer. Gatiss was also a friend of Diana Rigg. One evening, Gatiss had dinner with Stirling and Rigg and knowing that mother and daughter had never acted together, he mooted the idea of including characters written especially for them. Stirling was enthusiastic, while Rigg ,who had never seen the series, and rarely appeared in episodic television, was persuaded after viewing a showreel of the programme's iconic villains which had been assembled by The Recruiting Officer's stage manager, Michael Dennis.