“Good question, Isaac.” Vermishank’s manner was changing. He sounded more and more as if he was giving a seminar. Even in a situation like this, realized Isaac, the didactic instinct was strong in the old bureaucrat. “We simply don’t know. We’ve done all manner of experiments, with double-mirrors, treble-mirrors and so on. We don’t know why, but seeing them reflected negates the effect, even though it is formally an identical sight, as their wings are already mirrored in each other. But, and this is very interesting, reflect it again—look at them through two mirrors, I mean, like a periscope—and they can hypnotize you again. Isn’t that extraordinary?” He smiled.

Isaac paused. There was, he realized, something almost urgent about Vermishank’s manner. He seemed anxious to leave nothing out. It must have been Lemuel’s unwavering pistol.

“I’ve . . . seen one of these things feeding . . .” said Isaac. “I saw it . . . eat someone’s brain.”

“Hah.” Vermishank shook his head appreciatively. “Astonishing. You are lucky to be here. You did not see it eat anyone’s brain. Slake-moths don’t live entirely in our plane. Their . . . ah . . . nutritional needs are met by substances that we cannot measure. Don’t you see, Isaac?” Vermishank gazed at him intently, like a teacher trying to encourage the right answer from a petulant pupil. The urgency flashed again in his eyes. “I know biology’s not your strong point, but it’s such an . . . elegant mechanism, I thought you might see it. They draw the dreams out with their wings, flood the mind, break the dykes that hold back hidden thoughts, guilty thoughts, anxieties, delights, dreams . . .” He stopped. Sat back. Composed himself.

“And then,” he continued, “when the mind is nice and juicy . . . they suck it dry. The subconscious is their nectar, Isaac, don’t you see? That is why they only feed on the sentient. No cats or dogs for them. They drink the peculiar brew that results from self-reflexive thought, when the instincts and needs and desires and intuitions are folded in on themselves and we reflect on our thoughts and then reflect on the reflection, endlessly . . .” Vermishank’s voice was hushed. “Our thoughts ferment like the purest liquor. That is what the slake-moths drink, Isaac. Not the meat-calories slopping about in the brainpan, but the fine wine of sapience and sentience itself, the subconscious.

“Dreams.”

The room was silent. The idea was stunning. Everyone seemed to reel at the notion. Vermishank seemed almost to be revelling in the effect his revelations were having.

Everyone started at a clanging sound. It was just the construct, busy vacuuming the rubbish beside David’s desk. It had tried to empty the bin into its receptacle, had slightly missed and spilled the contents. It was busy trying to clear up the pieces of crumpled paper that surrounded it.