MAKING THE CHAMBER
Cut out the bottom of a large box, leaving a lip on three sides. Cut the false bottom from another piece of cardboard, fitting it inside the box and attaching it with a hinge of strong tape. Tape on a handle. Cut or tape together a one-piece cardboard top. For extra drama, paint the chamber black.
THE TRICK
Your Magic Chamber has a false bottom. When you tip the box forward, the box slides over your brother, who simultaneously is pulling the hinged bottom shut (by holding its handle).
Your hunched brother is now obscured behind the box. But to the audience, he's disappeared.
