During filming Elisabeth Sladen casually leaned on the TARDIS prop, which promptly collapsed on top of her. She was not seriously injured but the prop had to be replaced.
This story drew on numerous inspirations, including The Quatermass Experiment (1953), The Day of the Triffids (1963), The Thing from Another World (1951) and The Avengers (1961).
John Challis, who later achieved his greatest fame in the sitcom Only Fools and Horses (1981), has called this "one of the happiest jobs" he ever did.
The music by Geoffrey Burgon was created by five musicians playing a combination of flute, clarinet, harp, violin, cello, clavichord and percussion.
Fans voted this number 11 in a countdown of the 163 Doctor Who (1963) stories in Outpost Gallifrey's 40th anniversary poll in 2003.