The dream potion Carl and Katia drink together, which leaves them loopy and lets Carl's mind slip its bindings.
Carl and Katia take the potions as part of the plan for Carl to experience a dream from Shi Maria's point of view while Katia faces her own dream alone. Both go a little loopy, and in that moment Carl feels the plastic wrapping around his mind vanish and his reach extend beyond what it is supposed to be.
The result is a failure of separation. Carl and Katia touch hands, Edgar shouts, Imani pulls them apart, and the potions carry Carl into Katia's dream anyway through The Second Connection. Later Shi Maria's dream collides with theirs as well, so all three end up tangled in one place.
Not described in this chapter beyond being drunk before sleep.
The consumable that enables guided dream diving, and the cause of the accidental mind bleed.