After breaking through the wall and entering the secret room behind the bookshelf, the thieves immediately realized they were exposed: a mechanism dropped from the ceiling.
This mechanism was just a wooden pole, with the top fixed to the beam, and it could rotate around an axis. The bottom seemed to have something tied to it. When Li Long sounded the alarm, the whole house shook, breaking the suspension wire of the wooden pole mechanism, allowing it to swing down like a pendulum, stopping at the lowest point, and letting the attached item fly into the Secret Realm.
A very simple mechanism, but enough to thwart their plans completely. The wooden pole was completely flush with the beam, and even after examining the sandbox for three days, Yan Qing and his companions didn't notice anything unusual, all treating it as part of the beam.
