In TV science fiction, sometimes you can be working on a cracking idea for a monster costume, and only realise afterwards that there’s a silly detail that, while helping to define the character you’re creating, also unravels them a little. Like the Tereleptils, once-only enemies of the Fifth Doctor (in a story called The Visitation). On the face of it, they’re classic Whovian baddies, being reptilian and hoarse of throat, having clawed hands and scaly flesh, but then, looking at them, you realise they’re standing up awfully straight and stiff, and walking around as if they’re in dire need of the bathroom, and their heads are sort of leaning forwards as if they’re carrying a heavy weight on their backs. And then you look again and the penny drops....
