Once it's locked, the upper lever unfolds the wings.

It has long been their belief... that a whistle pitched at the precise resonant frequency of a metal lock... will vibrate the levers in such a way that the door will simply swing open.

It has long been their belief... that a whistle pitched at the precise resonant frequency of a metal lock... will vibrate the levers in such a way that the door will simply swing open.

It has long been their belief... that a whistle pitched at the precise resonant frequency of a metal lock... will vibrate the levers in such a way that the door will simply swing open.