It's curious in the extreme to me that a few lines on a bit of paper can look like what it is, a few flat lines on a flat bit of paper. But add a few extra lin

It's curious in the extreme to me that a few lines on a bit of paper can look like what it is, a few flat lines on a flat bit of paper. But add a few extra lines, and maybe a bit of shading and suddenly all I can see is a 3D image... I cant "see" the 2D lines anymore...