As with most magic tricks performed by professional musicians, the act of sawing a woman in half is a popular illusion and a mainstay in traditional magic shows. It is a tricky illusion that is accomplished with the use of trap doors, mirrors and, often, multiple women hidden in the box.
Although different "magic" boxes and magicians perform this trick in various ways, many rely on a trusted method involving two parts: two women, one of whom is hidden from the audience's view within a platform beneath the box and a special box that contains a hidden platform beneath, trap doors and movable sides.
The trick is done by one woman hiding within the platform beneath the box. This woman is often flexible and thin enough to fit in tight spaces without being obvious or visible to the audience. A second woman then "volunteers" to lie inside the box. Often, the magician will make a point to show the audience, with the use of the moveable sides of the box, that the woman is inside the box and that her head and feet are sticking out of the box.
Once the volunteer is secured inside, the hidden woman then allows her feet to stick out. This allows the visible woman to curl her feet up inside the head-end of the box, while the hidden woman is securely in the foot-end of the box. When the magician slices through the box with his saw, both women are safe and whole. All the audience sees is the appearance of the one visible woman being sawed in half.