You display a small block with a picture of Houdini on it and place it into in a clear tube. Now water is poured into the tube until Houdini is totally submerged.
The tube is covered with a borrowed handkerchief. After a few magic words the handkerchief is removed and Houdini has magically disappeared!
He then appears from inside your pocket.
The apparatus stands roughly twelve inches high and the clear tube measures approximately one inch in diameter.