So if he whispers in the head’s left ear, we hear it in our left ear. If he circles behind it, we hear him behind us, even though we can see him in front of us. Creaks, clanks and a whispering voice – scream-king Mark Gatiss, uncredited – leak directly into our skulls, while an ominous heartbeat seems periodically to throb through the very fabric of the theatre. Jonathan Livingstone’s blokey engineer, in the windowed control room behind Blagden, is mostly shrouded in darkness, but sudden blasts of light and bursts of sound reveal… well, that would be telling. Suffice to say it’s very, very creepy.