Filming locations: Trefil Quarry, Brecon Beacons (opening and closing scenes); RAF Saint Athan (the battery farm)

The Doctor: Set the controls to random. Mystery tour. Outside that door could be any planet, anywhere, any when in the whole wide… are you alright?
Donna: Terrified. I mean, history's one thing but an alien planet…
The Doctor: I could always take you home.
Donna: Yeah, don't laugh at me.
The Doctor: I know what it's like. Everything you're feeling right now, the fear, the joy, the wonder, I get that.
Donna: Seriously? After all this time?
The Doctor: Yeah! Why do you think I keep going?

(trapped in handcuffs)
Donna: Well, do something. You're the one with all the tricks. You must have met Houdini.
The Doctor: These are really good handcuffs.
Donna: Well I'm glad of that. I mean, at least we've got quality!

Donna: It's weird, but being with you, I can't tell what's right and what's wrong anymore.
The Doctor: It's better that way. People who know for certain tend to be like Mr. Halpen.

The Doctor: Oh, I've sort of got a song of my own, thanks.
Ood Sigma: I think your song must end soon.
The Doctor: Meaning?
Ood Sigma: Every song must end.
The Doctor: ...yeah.

Donna: A great big empire built on slavery
The Doctor: It's no so different from your time
Donna: Oh! I ain't got slaves
The Doctor: Who do you think made your clothes ?

The Ood picture in the background of Bartle's office is based on Andy Warhol's 60s pop art prints.

The Ood previously appeared in "The Impossible Planet" and "The Satan Pit", where the "red eye" indicated that they had been possessed by the Devil.

The Doctor mentions that Ood-Sphere is near Sense-Sphere. Sense-Sphere is the home planet of the Sensorites, who first appeared in "Strangers in Space" (1964) in the original Doctor Who series.