The magician tells the audience about his recent visit to an old Victorian house, believed to be haunted. He shows the audience a souvenir from his visit: a large brass bolt and nut. The nut is screwed onto the bolt and everything is placed on the table. The magician covers the nut and bolt for just a moment with a silk handkerchief and when the cover is removed, the audience can see the bolt has unscrewed itself from the nut!
This is 100% mechanical and the prop has been beautifully made. A true mechanical marvel that is super easy to perform.