A side passage opened after Wei followed a pulse of light along the west wall. He had been checking the chalk marks against the new survey when one pale thread moved away from the chamber and ran toward a narrow seam.
“Don’t touch it yet,” Gu said.
Wei held his hand a finger’s width from the wall. The light faded, then returned when he shifted his weight. “It’s responding to me.”
“Or to the movement,” Yan said. His cheek dressing tugged when he turned his head. The cut had stopped bleeding, but the skin remained tender.
Luo looked from the seam to the corridor. “We open it only as far as the outer chamber.”
The stone panel slid aside with a soft click. Beyond it lay a room where thin metal blades swung from hidden joints. They were narrow enough to hide in the wall grooves, and the old oil on their pivots made almost no sound.
Wei watched two cycles before moving. The blades swept across the room, paused, then returned. Each footfall seemed to change the timing.
“Sound,” he said. “They respond to the sound of a step.”
