It likely goes without saying that Childermass sits up when Lambert does, if not sooner. He doesn't bother trying to get to his feet just yet, which leaves the witcher with someone sitting on his lap for a moment longer, but who cares about that? It worked. It had to have. That's the very trick he's been trying to pull off since observing not just Strange and his mirrors, but from Joker's little teleportation trinket and even what the Warden could do, though obviously tying it to something besides math and coordinates and the like.

Shadows seemed thematic with him, anyhow, so it was natural to go with them.

"I can't believe it," he starts, but with a laugh rather than actual disbelief in his voice. He turns enough to look back at Lambert, a triumphant grin spreading across his face not unlike how he would grin back during the Celebration, only this time it's all on his own, no drink or drugs or enchantment required. "It actually worked! I've been trying to do that for weeks and it took this, of all things..."

It makes enough sense. Faerie magic is supposedly more attuned to wanting something to happen than having a laundry list of specific words, devices, and ritual to go through. Nearly getting their necks broken, that seems like a sure cause for triggering it.