"It's a reactive show," he says. "So you're not acting - you're reacting. And so the director will often say 'right, this is what you're doing now, this is how you need to act at this precise moment, because this thing is coming at ya.' And we have to go, 'What does it look like?'" And one time the director went 'we don't know yet!' There's nothing to react to. So I remember I walked out of wherever we were, and I had to walk out one building and come out and they said, 'right, so you've gotta look at this thing and you gotta be in awe of this massive great thing.' And I've come out, and I've gone [he mimes awe] 'Oh, wow!' Next thing I hear is: 'Cut!'
"They said 'What are you doing? What are you looking at?' I went 'I'm looking at the thing.' She went 'No no no no no, it's over there!' I look back at the rushes, and I'm the only one going, 'awwww'. I'm thinking I look like such an idiot. I'm looking in totally the wrong area because I haven't paid attention, I didn't have it in my head what it was supposed to be. So they're all staring that way and I'm looking at something totally different. And that's what happens. You don't actually know, because they haven't green screened it yet, the monster hasn't been developed. They'll put it in after, basically."
Walsh, who plays companion Graham O'Brien, previously told RadioTimes.com that he was originally hesitant to take on the role – mainly because Chris Chibnall wouldn't reveal to him who the Thirteenth Doctor was going to be – but was sold by the producers' pitch that the new series was going to be influenced by Star Trek.
"I remember what the phrase was which helped sell it a while after I found out it was Doctor Who," he says. "They said: 'It's an ensemble piece, Brad. You're not going to be the Doctor.' I went, 'well that's good, because I don't understand any gobbledegook'. I said, 'Who is going to be the Doctor then?' And they went 'We don't know yet, we haven't chosen them.' I went, 'Oh, OK, fine. OK, cool.'
"A week later – who's the Doctor? 'Dunno, we haven't chosen them yet.' And that went on and on and on. And I said 'How can I gauge what I'm going to do with the part?'And they said 'You're gonna be like an older companion. And it's gonna be a bit like the bridge on the Enterprise. It's gonna be an ensemble piece. It's gonna be like...' And I went 'I'm in!' as soon as they said that, because I'm a massive Trekkie. I went 'I'm in, I'm in, that's it, OK done it'."
Doctor Who series 11 will premiere on BBC1 on October 7
