This was the last regular episode (as opposed to minisode or online prequel) to use the fifth/sixth-season opening credits sequence.
Bill Bailey was pleased to be given a comedic human character, explaining, "The fact that I am almost playing a human means the expressions are easier to do. If I was an Ood, with a face full of tentacles, that would have been harder to bring the funny".
The story partly takes place on Androzani Major. The Fifth Doctor's final story The Caves of Androzani: Part Four (1984) took place on Androzani Minor.
There were numerous references to C.S. Lewis' "The Lion, the Witch, and the Wardrobe," namely: (a) the three-part name itself ("The Doctor, the Widow, and the Wardrobe"), (b) the family (children) going to a large mansion in the country to escape the bombing in London, (c) "Digby" sounds a lot like "Digory," Professor Kirk's first name, (d) the Doctor refers to the TARDIS as his "wardrobe," (e) there is a snow-covered woods on the other side of the box, (f) time moves differently on the other side of the box, (g) the line "What do they teach these children...?", (h) the door knocker on the tree house resembled a lion, and (i) the spirits of the trees were sentient in Narnia as well.
Matt Smith's iconic hairstyle for the Eleventh Doctor had to be contained somewhat in order to fit in the helmet of the spacesuit he was wearing in this episode. A behind-the-scenes photo shows this resulting in a bizarre style of "helmet hair"