Metamorphosis is a stage illusion (magic trick) invented by John Nevil Maskelyne (who also invented the first typewriter to be produced in Great Britain), but most often associated with famous magician and escape artist Harry Houdini, and performed to some reknown (for speed) by The Pendragons, among many others.
In the illusion, an assistant (Houdini employed his wife Bess) is locked inside a large box or trunk, often after being restrained with handcuffs, ropes, bags, etc. The magician stands upon the trunk and holds a curtain up to momentarily conceal his entire body. The curtain is immediately lowered, revealing that the assistant is now standing atop the box, the magician and assistant having changed places instantaneously. When the box is opened, it is shown to contain the magician, restrained as the assistant had been.
The Metamorphosis uses a device known as the substitution trunk, which has a secret panel that allows its occupant to sneak out.
Having extricated himself from the sack in which he was tied, Houdini would climb out of the hidden door and crouch behind a curtain lifted by his wife.
The two would quickly change places, Houdini appearing behind the curtain as Bess disappeared into the box.
Bess would then emerge from the box and sack wearing a different costume.
