Suppose you have a piece of paper in the shape of a left shoe, on a flat surface. Suppose also that it can only stay in contact with the surface. No matter how you move it or rotate it in the 2D surface, it cannot become a right shoe. However, if you move it out of the 2D space, flip it and return it to the flat surface, it will now become a right shoe. By analogy, could we move a real left shoe into 4D space, 'rotate' it properly and obtain a right shoe for the other foot??? Would this be possible with the curving of 3D space?