Anybody can cut a human being in half, but seemingly it's only magicians who are able to do it without killing the person involved in the process. Not only that, they can put them back together again moments later!
There are always two people involved in this trick, and both of them are skilled contortionists. They fold themselves up inside the cramped space within the boxes and give the illusion of being one body. It's uncomfortable, but it isn't impossible.