A brass combination lock is handed out and examined by thespectator which cannot be opened without the secret 4 digit number combination.The magician explained that this magic lock can only be opened with the spectator's year of birth whoever touches it.The spectator goes on to try open the lock herself using her birthday year, and it is the correct secret combination.The lock opens.End of story. Or 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.The spectator goes on to try open the lock herself using her birthday year, and it is the correct secret combination.The lock opens. Can guess numbers such as someone’s year of birth, anniversary or birthday.