Henstridge: When we first went into the audition, we got very little information. We got that they kind of came as a duo, and that Simmons was a biochemist and she was incredibly intelligent, but that’s kind of all I got. That she was young and intelligent. And then you just get the script, that’s specifically for the auditions.

Loeb: We didn’t want to use a scene from the actual pilot for a number of reasons. One of which was that as executive producers we didn’t want to be sick of the scene by the time we were going to shoot it, and we were seeing hundreds of actors from Toronto and London and New York and Australia and Los Angeles… Joss wrote a scene specifically for the audition — basically, the two of them in a very close, trapped space, and they’re going to die. We saw each of them individually, and then we picked pairs. I think what it really speaks to is that Elizabeth and Iain, in their very first reading together, had a kind of chemistry that we weren’t going to be able to manufacture; it just happened. They’re very different sorts of people, and that magic happened right away, and just made it sort of easy.

- from a Wired interview last fall (x)