"The trick of the film, the way that the film intends to work is to present something which is unambiguously a machine and then gradually remove your sense of Ava being a machine, even while you continue to see her being that way. And the sound design is a key part of that. You can hear ... the sounds of the bits of machinery moving, which aren't specified. They're not quite gears and cogs and pistons, they're something slightly odder than that. And there's also this pulse which is not dissimilar in some respects to a heartbeat, although it isn't a heartbeat."