Impossible Lock - Spectator Predict
A borrowed ring is locked on a 4 digit combination brass lock and, the dials are mixed.
Spectator can test that the lock cannot be opened.
Spectator thinks of a 4 digit number & dials them on the lock.
This proves to be the secret numbers that opens the lock!
Mechanical, nothing to break
Spectators set the chosen numbers on the lock!
They open it themselves!